[nextpage title=”Introduction”]

We also like to review low-end products from time to time so people with a serious budget restriction can have an idea whether it is worthwhile to buy cheap products or not. Today we are going to take an in-depth look at eXtreme Power Plus 550 W (RS-550-PCAR-E3) from Cooler Master. Can it really deliver its rated power? Let’s see.

We’ve already reviewed the 400 W (RS-400-PCAR-A3), the 460 W (RS-460-PMSR-A3) and the 500 W (RS-500-PCAR-A3) models from this same series. The 400 W and the 500 W models were able to deliver their labeled wattages, but both presented very high noise and ripple on their outputs. And the 460 W model wasn’t capable of delivering its labeled capacity. Let’s see the fate of this 550 W model.

While other members of eXtreme Power Plus series are manufactured by AcBel Polytech, this particular unit is manufactured by Seventeam, just like members from an older series called eXtreme Power (without the “Plus”) – in fact it is a renamed Seventeam ST-500BAZ power supply. Our guess is that the "A3" at the end of the part number indicates the first manufacturer, while "E3" indicates the second.

By the way, like other members from this series the reviewed unit has the fantastic “As sealed stick was removed, lost or damaged, it shall be out of warranty validity” statement on its label. When Chinese manufacturers will stop using on-line translators and hire someone that can speak English to write their labels?

An interesting thing is that on the power supply label there is no information about the unit’s maximum wattage (the “550” number is printed without the letter “W” after it). Hum…

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 1: Cooler Master eXtreme Power Plus 550 W power supply.

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 2: Cooler Master eXtreme Power Plus 550 W power supply.

Cooler Master eXtreme Power Plus 550 W is 5 ½” (140 mm) deep, using a 120 mm fan on its bottom. This unit does not feature a PFC circuit, as you can see by the presence of a 115 V/230 V switch in Figure 1, but at least it is being based on a more modern design than the outdated half-bridge topology, as we will show.

No modular cabling system is provided and only the main motherboard cable have a nylon protection that come from inside the power supply housing. All cables use 18 AWG wires, which is the correct gauge to be used and an improvement over the models with lower wattage from this series, which use thinner 20 AWG wires. The cables included are:

  • Main motherboard cable with a 20/24-pin connector, 17 ¾” (45 cm) long.
  • One cable with two ATX12V connectors that together form one EPS12V connector, 21 ¼” (54 cm) long.
  • Two cables with one six/eight-pin connector for video cards each, 18 1/8” (46 cm) long.
  • Two cables with three SATA power connectors each, 18 1/8” (46 cm) to the first connector, 5 7/8” (15 cm) between connectors.
  • One cable with three standard peripheral power connectors and one floppy disk drive power connector, 18 1/8” (46 cm) to the first connector, 5 7/8” (15 cm) between connectors.

This configuration is compatible with a product on the 550 W range and was overly improved in comparison to the 500 W model, with more connectors (especially a second video card connector) and greater length.

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 3: Cables.

Now let’s take an in-depth look inside this power supply.

[nextpage title=”A Look Inside The Cooler Master eXtreme Power Plus 550 W”]

We decided to disassemble this power supply to see what it looks like inside, how it is designed, and what components are used. Please read our Anatomy of Switching Power Supplies tutorial to understand how a power supply works and to compare this power supply to others.

This page will be an overview, and then in the following pages we will discuss in detail the quality and ratings of the components used. Since the 550 W model is manufactured by a different company than the one responsible for the lower-wattage eXtreme Power Plus models, its internal design is obviously very different from the lower-wattage members from this family.

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 4: Overall look.

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 5: Overall look.

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 6: Overall look.

[nextpage title=”Transient Filtering Stage”]

As we have mentioned in other articles and reviews, the first place we look when opening a power supply for a hint about its quality, is its filtering stage. The recommended components for this stage are two ferrite coils, two ceramic capacitors (Y capacitors, usually blue), one metalized polyester capacitor (X capacitor), and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components, usually removing the MOV and the first coil. 

This unit is flawless on this stage, with all required components plus four extra Y capacitors, one extra ferrite coil and one extra X capacitor.

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 7: Transient filtering stage (part 1).

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion about the components used in the Cooler Master eXtreme Power Plus 550 W.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of Cooler Master eXtreme Power Plus 550 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBU1006 rectifying bridges connected in parallel, each one supporting up to 10 A at 100° C. At 115 V this unit would be able to pull up to 2,300 W from the power grid; assuming 80% efficiency, the bridges would allow this unit to deliver up to 1,840 W without burning themselves out. Of course, we are only talking about these components, and the real limit will depend on all the other components in this power supply. It is always nice to see a huge overspecification like this one.

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 9: Rectifying bridges.

This unit is based on a single-transistor forward topology, which is good to see, since usually low-end units are based on the obsolete half-bridge design. Two 2SK2611 power MOSFETs are connected in parallel on the switching section in order to double the maximum current this section can handle. Each transistor supports up to 9 A at 25° C in continuous mode, or up to 27 A at 25° C in pulse mode, so the switching section can deliver up to 18 A at 25° C. Unfortunately the manufacturer does not provide the current limits at 100° C. These transistors present an RDS(on) of 1.1 Ω, which is insanely high (low efficiency). This number measures the resistance provided by the transistors when they are turned on; the lower this number, the better (higher efficiency). These are the same transistors used on eXtreme Power Plus 500 W, even though this other model is manufactured by a different company.

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 10: One of the switching transistors.

The switching transistors are controlled by a TL3842 PWM controller, which is located on the primary.

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 11: PWM controller.

The two electrolytic capacitors from the voltage doubler are from Su’scon and labeled at 85° C.

Now let’s take a look at the secondary of this power supply.

[nextpage title=”Secondary Analysis”]

This power supply has five Schottky rectifiers on its secondary.

The maximum theoretical current each line can deliver is given by the formula I / (1 – D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode. Just as an exercise, we can assume a typical duty cycle of 30%.

The +12 V output is produced by two S30D150C Schottky rectifiers, each one supporting up to 30 A (15 A per internal diode at 100° C, 0.95 V maximum voltage drop), giving us a maximum theoretical current of 43 A or 514 W for the +12 V output.

The +5 V output is produced by one SBL6040PT Schottky rectifier, which supports up to 60 A (30 A per internal diode), giving us a maximum theoretical current of 43 A or 214 W for the +5 V output.

The +3.3 V output is produced by two SBL3040PT Schottky rectifiers connected in parallel, each one supporting up to 30 A (15 A per internal diode), giving us a maximum theoretical current of 43 A or 141 W for the +3.3 V output.

One curious thing we noticed was the presence of a -5 V output (white wire), that has been removed from the ATX12V specification in January 2002. Interesting enough this unit is labeled as being an ATX12V 2.3 model.

All these numbers are theoretical. The real amount of current/power each output can deliver is limited by other components, especially by the coils used on each output.

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 12: +3.3 V, +5 V and +12 V rectifiers.

The outputs are monitored by a WT7510 integrated circuit, which supports only OVP (over voltage protection) and UVP (under voltage protection) protections.

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 13: Monitoring integrated circuit.

The electrolytic capacitors from the secondary are also from Su’scon.

[nextpage title=”Power Distribution”]

In Figure 14, you can see the power supply label containing all the power specs.

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 14: Power supply label.

As you can see, according to the label this unit has two +12 V rails. Inside the unit the +12 V wires are separated into two different groups, connected to individual filtering stages. Although this is a terrific configuration, there is no over current protection monitoring each rail. The two groups are divided like this:

  • +12V1 (solid yellow wire): Main motherboard cable, SATA power cables, peripheral power cable and one of the video card power cables.
  • +12V2 (yellow with black stripe wire): ATX12V/EPS12V cable and one of the video card power cables.

If you are going to install a video card with just one auxiliary power connector, install it to the connector using solid yellow wires. This way you are going to keep the video card separated from the CPU.

Now let’s see if this power supply can really deliver 550 W.

[nextpage title=”Load Tests”]

We conducted several tests with this power supply, as descri
bed in the article Hardware Secrets Power Supply Test Methodology.  

This time we made more detailed tests, starting from 85 W and increasing load little by little until we could see the maximum amount of power we could extract from the reviewed unit.

If you add all the power listed for each test, you may find a different value than what is posted under “Total” below. Since each output can vary slightly (e.g., the +5 V output working at +5.10 V), the actual total amount of power being delivered is slightly different than the calculated value. On the “Total” row we are using the real amount of power being delivered, as measured by our load tester.

The +12VA and +12VB inputs listed below are the two +12 V independent inputs from our load tester. During this test the +12VA input was connected to the power supply “+12V1” rail, while +12VB was connected to the power supply “+12V2” rail (EPS12V connector).

Input Test 1 Test 2 Test 3 Test 4 Test 5
+12VA 3 A (36 W) 3.5 A (42 W) 4.5 A (54 W) 5.5 A (66 W) 6.25 A (75 W)
+12VB 2.5 A (30 W) 3.25 A (39 W) 4 A (48 W) 5 A (60 W) 6 A (72 W)
+5V 1 A (5 W) 1 A (5 W) 1.5 A (7.5 A) 1.5 A (7.5 A) 2 A (10 W)
+3.3 V 1 A (5 W) 1 A (5 W) 1.5 A (4.95 W) 1.5 A (4.95 W) 2 A (6.6 W)
+5VSB 1 A (5 W) 1 A (5 W) 1 A (5 W) 1 A (5 W) 1 A (5 W)
-12 V 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W)
Total 84.6 W 99.2 W 124.4 W 147.8 W 172.7 W
% Max Load 15.4% 18.0% 22.6% 26.9% 31.4%
Room Temp. 41.6° C 41.2° C 41.1° C 41.5° C 41.9° C
PSU Temp. 44.9° C 44.9° C 44.9° C 44.9° C 45.1° C
Voltage Regulation Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 123.3 W 139.8 W 169.8 W 197.1 W 227.5 W
Efficiency 68.6% 71.0% 73.3% 75.0% 75.9%
AC Voltage 116.2 V 116.0 V 115.7 V 115.4 V 115.2 V
Power Factor 0.638 0.643 0.655 0.664 0.673
Final Result Pass Pass Pass Pass Pass
Input Test 6 Test 7 Test 8 Test 9 Test 10
+12VA 7.5 A (90 W) 8.25 A (99 W) 9.25 A (111 W) 10 A (120 W) 11 A (132 W)
+12VB 7 A (84 W) 8 A (96 W) 9 A (108 W) 10 A (120 W) 11 A (132 W)
+5V 2 A (10 W) 2.5 A (12.5 W) 2.5 A (12.5 W) 3 A (15 W) 3 A (15 W)
+3.3 V 2 A (6.6 W) 2.5 A (8.25 W) 2.5 A (8.25 W) 3 A (9.9 W) 3 A (9.9 W)
+5VSB 1 A (5 W) 1 A (5 W) 1 A (5 W) 1 A (5 W) 1 A (5 W)
-12 V 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W)
Total 198.7 W 223.5 W 246.5 W 270.9 W 293.5 W
% Max Load 36.1% 40.6% 44.8% 49.3% 53.4%
Room Temp. 43.2° C 44.2° C 45.2° C 46.5° C 45.4° C
PSU Temp. 46.0° C 46.7° C 47.6° C 48.9° C 49.9° C
Voltage Regulation Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 259.1 W 290.4 W 318.4 W 349.4 W 378.6 W
Efficiency 76.7% 77.0% 77.4% 77.5% 77.5%
AC Voltage 114.6 V 114.1 V 113.6 V 113.1 V 113.3 V
Power Factor 0.679 0.685 0.687 0.693 0.697
Final Result Pass Pass Pass Pass Pass
Input Test 11 Test 12 Test 13 Test 14 Test 15
+12VA 12 A (144 W) 13 A (156 W) 14 A (168 W) 15 A (180 W) 16 A (192 W)
+12VB 11.75 A (141 W) 12.75 A (153 W) 13.5 A (162 W) 14.5 A (174 W) 15.5 A (186 W)
+5V 3.5 A (17.5 W) 3.5 A (17.5 W) 4 A (20 W) 4 A (20 W) 4.5 A (22.5 W)
+3.3 V 3.5 A (11.55 W) 3.5 A (11.55 W) 4 A (13.2 W) 4 A (13.2 W) 4.5 A (14.85 W)
+5VSB 1 A (5 W) 1 A (5 W) 1 A (5 W) 1 A (5 W) 1 A (5 W)
-12 V 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W)
Total 318.2 W 340.5 W 364.4 W 386.9 W 412.6 W
% Max Load 57.9% 61.9% 66.3% 70.3% 75.0%
Room Temp. 44.5° C 46.6° C 48.5° C 45.7° C 47.3° C
PSU Temp. 46.9° C 48.5° C 50.6° C 52.3° C 54.3° C
Voltage Regulation Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 411.5 W 442.9 W 474.0 W 506.0 W 543.0 W
Efficiency 77.3% 76.9% 76.9% 76.5% 76.0%
AC Voltage 113.4 V 112.6 V 112.7 V 112.3 V 112.1 V
Power Factor 0.702 0.703 0.705 0.708 0.710
Final Result Pass Pass Pass Pass Pass
Input Test 16 Test 17 Test 18 Test 19 Test 20
+12VA 17 A (204 W) 18 A (216 W) 19 A (228 W) 20 A (240 W) 21 A (252 W)
+12VB 16.5 A (198 W) 17.25 A (207 W) 18.5 A (222 W) 19 A (228 W) 20 A (240 W)
+5V 4.5 A (22.5 W) 5 A (25 W) 5 A (25 W) 5.5 A (27.5 W) 5.5 A (27.5 W)
+3.3 V 4.5 A (14.85 W) 5 A (16.5 W) 5 A (16.5
W)
5.5 A (18.15 W) 5.5 A (18.15 W)
+5VSB 1 A (5 W) 1 A (5 W) 1 A (5 W) 1 A (5 W) 1 A (5 W)
-12 V 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W)
Total 435.4 W 458.7 W 484.3 W 503.4 W 549.4 W
% Max Load 79.2% 83.4% 88.1% 91.5% 99.9%
Room Temp. 44.3° C 47.1° C 44.8° C 45.5° C 49.4° C
PSU Temp. 50.9° C 54.2° C 46.7° C 47.0° C 51.2° C
Voltage Regulation Pass Pass Pass Pass Fail on +12 V
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 576.0 W 613.0 W 651.0 W 688.0 W Fail
Efficiency 75.6% 74.8% 74.4% 73.2% Fail
AC Voltage 111.2 V 110.8 V 110.5 V 110.1 V Fail
Power Factor 0.713 0.715 0.717 0.720 Fail
Final Result Pass Pass Pass Pass Fail

Cooler Master eXtreme Power Plus 550 W burned while we tried to pull 550 W from it at high temperatures.

Efficiency was always below 80%, varying between 73.2% and 77.5%, depending on the load.

Voltages were always within the allowed range.

And noise and ripple levels were always low. Below we publish the results for the test 20 (550 W), however it is important to notice that noise levels jumped from the ultra-low 25.2 mV at +12VA on test 19 to 78.4 mV on test 20. The same thing happened with the other outputs (noise level at +5 V jumped from 18.8 mV to 43.6 mV, for example). The maximum allowed is 120 mV on +12 V outputs and 50 mV on +3.3 V and +5 V outputs. All numbers are peak-to-peak figures.

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 15: +12VA input from load tester at 549.4 W (78.4 mV).

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 16: +12VB input from load tester at 549.4 W (88.2 mV).

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 17: +5 V rail with power supply delivering 549.4 W (43.6 mV).

Cooler Master eXtreme Power Plus 550 W RS-550-PCAR-E3 power supplyFigure 18: +3.3 V rail with power supply delivering 549.4 W (12.2 mV).

[nextpage title=”Main Specifications”]

Cooler Master eXtreme Power Plus 550 W power supply specs include:

  • ATX12V 2.3
  • Nominal labeled power: 550 W
  • Measured maximum power: 503.4 W at 45.5° C.
  • Labeled efficiency: Above 70%
  • Measured efficiency: Between 73.2% and 77.5% at 115 V (nominal, see complete results for actual voltage).
  • Active PFC: No.
  • Modular Cabling System: No.
  • Motherboard Power Connectors: One 20/24-pin connector and two ATX12V connectors that together form an EPS12V connector.
  • Video Card Power Connectors: Two six/eight-pin connectors in separated cables.
  • SATA Power Connectors: Six in two cables.
  • Peripheral Power Connectors: Three in one cable.
  • Floppy Disk Drive Power Connectors: One.
  • Protections: over voltage (OVP), over power (OPP) and short-circuit (SCP). Under voltage protection (UVP) present but not listed by the manufacturer.
  • Warranty: Information not available.
  • Real Model: Seventeam ST-500BAZ
  • More Information: https://www.coolermaster-usa.com
  • Average price in the US*: USD 65.00.

* Researched at Newegg.com on the day we published this review.

[nextpage title=”Conclusions”]

Although some can see Cooler Master eXtreme Power Plus 550 W as an option if you are not going to pull 550 W from it, we can’t recommend this unit, as it burns if you try to pull its rated wattage. Its main technical problem is efficiency, between 73.2% and 77.5%, which would prevent us from recommending this unit even if it could deliver its labeled power.

But there is another problem: pricing. Costing USD 65 it is simply too expensive for what it is. For the same price you can buy an OCZ StealthXStream 500 W, which provides higher efficiency.

You see, this unit is a renamed Seventeam ST-500BAZ, a 500 W power supply that has already been discontinued by the manufacturer – no wonder it couldn’t deliver its labeled power.