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[nextpage title=”Introduction”]

Purepower 500 W (W0100RU) is an entry-level power supply from Thermaltake. Is this a good pick for users on a tight budget? Let’s see.

This power supply is manufactured by CWT, being a rebranded PUF-405 from this manufacturer.

Analyzing the power supply label, something immediately caught our attention. In very small letters the manufacturer says that the maximum power from this unit is 405 W (which makes sense, as it is a rebranded 405 W unit, PUF-405 from CWT), with 500 W being the maximum peak power. We wonder why a well-known brand like Thermaltake would still use this sordid technique to deceive consumers.

Thermaltake Purepower 500 W power supplyFigure 1: Thermaltake Purepower 500 W power supply.

Thermaltake Purepower 500 W power supplyFigure 2: Thermaltake Purepower 500 W power supply.

Thermaltake Purepower 500 W is 5 ½” (140 mm) deep, using a 120 mm fan on its bottom. Although not having active PFC circuit, this unit is based on a modern design, as we will show later.

There is no modular cabling system and all cables have nylon sleevings that don’t come from inside the unit. All wires are 18 AWG, which is the correct gauge to be used. The cables included are:

  • Main motherboard cable with a 20/24-pin connector, 19 ¼” (49 cm) long.
  • One cable with two ATX12V connectors that together form an EPS12V connector, 20 7/8” (53 cm) long.
  • One cable with one six-pin connector for video cards, 20 ½” (52 cm) long.
  • One cable with four SATA power connectors, 19 ¾” (50 cm) to the first connector, 5 7/8” (15 cm) between connectors.
  • Two cables with four standard peripheral power connectors and one floppy disk drive power connector each, 20 ½” (52 cm) to the first connector, 5 7/8” (15 cm) between connectors.

This configuration is not bad for an entry-level product, although we’d like to see the SATA power connectors separated in two different cables instead of being all combined on a single cable.

Thermaltake Purepower 500 W power supplyFigure 3: Cables.

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

[nextpage title=”A Look Inside The Thermaltake Purepower 500 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.

Thermaltake Purepower 500 W power supplyFigure 4: Overall look.

Thermaltake Purepower 500 W power supplyFigure 5: Overall look.

Thermaltake Purepower 500 W 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 power supply is flawless on this stage, with two Y capacitors and one X capacitor more than the minimum required. The MOV’s are available between the electrolytic capacitors from the voltage doubler and thus not shown on the pictures below.

Thermaltake Purepower 500 W power supplyFigure 7: Transient filtering stage (part 1).

Thermaltake Purepower 500 W 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 Thermaltake Purepower 500 W.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of Thermaltake Purepower 500 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU806 rectifying bridge, which supports up to 8 A at 100° C if a heatsink is used or only up to 3.5 A at 100° C if a heatsink isn’t used, which is the case. At 115 V this unit would be able to pull up to 403 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 322 W without burning itself out. Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

Thermaltake Purepower 500 W power supplyFigure 9: Rectifying bridge.

The electrolytic capacitors from the voltage doubler circuit are from JunFu.

When analyzing the switching section from Thermaltake Purepower 500 W we had a good surprise. Usually power supplies without active PFC circuit are based on the half-bridge topology, which is currently considered obsolete. This unit, however, uses the two-transistor forward switching configuration, just like power supplies with active PFC, wh
ich – at least in theory – promises higher efficiency.

The switching transistors are from the MOSFET kind (and not “regular” transistors like half-bridge power supplies), with two STP14NK50Z being used. Each transistor can handle up to 14 A at 25° C or up to 7.6 A at 100° C in continuous mode (note the difference temperature makes) or up to 48 A at 25° C in pulse mode. There transistors present a 380 mΩ resistance when turned on, a parameter called RDS(on). The lower this number, the better, meaning that the transistor will consume less and thus present higher efficiency.

Thermaltake Purepower 500 W power supplyFigure 10: Switching transistors.

The switching transistors are controlled by a UC3845B PWM combo controller, which is located on the solder side of the printed circuit board.

Thermaltake Purepower 500 W power supplyFigure 11: PWM controller.

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

[nextpage title=”Secondary Analysis”]

This power supply has four Schottky rectifiers attached to its secondary heatsink.

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 STPS20H100CT Schottky rectifiers connected in parallel, each one supporting up to 20 A (10 A per internal diode at 160° C, 0.88 V maximum voltage drop). This gives us a maximum theoretical current of 29 A or 343 W for the +12 V output – a value that is simply too low for a model labeled as being a 500 W unit.

The +5 V output is produced by one STPS30L45CT Schottky rectifier, which is capable of delivering up to 30 A (15 A per internal diode at 135° C, 0.74 V maximum voltage drop), giving us a maximum theoretical current of 21 A or 107 W for the +5 V output.

The +3.3 V output is produced by a STPS3045CT Schottky rectifier, which is capable of delivering up to 30 A (15 A per internal diode at 155° C, 0.57 V typical voltage drop and 0.84 V maximum voltage drop), giving us a maximum theoretical current of 21 A or 71 W for the +3.3 V output.

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.

Thermaltake Purepower 500 W power supplyFigure 12: +12 V and +3.3 V rectifiers.

Thermaltake Purepower 500 W power supplyFigure 13: +5 V and +12 V rectifiers.

The outputs are monitored by a PS229 integrated circuit. Unfortunately no datasheet is available for this chip.

Thermaltake Purepower 500 W power supplyFigure 14: Monitoring integrated circuit.

All capacitors from the secondary are from Teapo.

[nextpage title=”Power Distribution”]

In Figure 15, you can see the power supply label containing all the power specs.

Thermaltake Purepower 500 W power supplyFigure 15: Power supply label.

As you can see, the label says this unit has two +12 V rails. Even though internally the +12 V (yellow) wires are divided into two groups, there are no current sensors (“shunts”), so this unit does not have over current protection, which is a prerequisite for a group of wires to be considered a “rail.” Read our tutorial on this subject to understand more.

Thermaltake Purepower 500 W power supplyFigure 16: No current sensors (“shunts”), therefore no over current protection.

Now let’s see if this power supply can really deliver 500 W.

[nextpage title=”Load Tests”]

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

Since we knew this unit wasn’t a 500 W unit, we tested it a little bit differently. Starting with an 85 W load pattern, we increased the loads little by little until we reached the maximum the unit could deliver.

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 both inputs were connected to the power supply single rail, with the +12VB input connected to the power supply 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 83.5 W 97.5 W 122.4 W 145.2 W 169.6 W
% Max Load 16.7% 19.5% 24.5% 29.0% 33.9%
Room Temp. 43.4° C 42.1° C 41.9° C 42.1° C 42.8° C
PSU Temp. 42.8° C 42.8° C 42.8° C 43.0° C 43.3° C
Voltage Regulation Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 101.2 W 117.6 W 147.2 W 173.8 W 204.2 W
Efficiency 82.5% 82.9% 83.2% 83.5% 83.1%
AC Voltage 113.0 V 117.7 V 113.3 V 113.2 V 112.7 V
Power Factor 0.596 0.608 0.639 0.653 0.670
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 194.8 W 218.9 W 241.1 W 264.9 W 286.5 W
% Max Load 39.0% 43.8% 48.2% 53.0% 57.3%
Room Temp. 44.3° C 45.5° C 46.6° C 48.0° C 49.8° C
PSU Temp. 44.5° C 45.4° C 46.3° C 47.6° C 49.3° C
Voltage Regulation Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 235.8 W 266.5 W 295.1 W 327.2 W 357.1 W
Efficiency 82.6% 82.1% 81.7% 81.0% 80.2%
AC Voltage 111.1 V 110.2 V 110.5 V 110.6 V 116.8 V
Power Factor 0.678 0.684 0.687 0.69 0.660
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 310.2 W 331.4 W 354.8 W 375.4 W Fail
% Max Load 62.0% 66.3% 71.0% 75.1% Fail
Room Temp. 43.8° C 44.4° C 44.6° C 45.6° C Fail
PSU Temp. 43.8° C 44.4° C 46.4° C 49.9° C Fail
Voltage Regulation Fail on +12 V Fail on +12 V Fail on +12 V Fail on +12 V Fail
Ripple and Noise Pass Pass Pass Pass Fail
AC Power 391.9 W 422.0 W 459.0 W 496.0 W Fail
Efficiency 79.2% 78.5% 77.3% 75.7% Fail
AC Voltage 116.5 V 116.6 V 116.1 V 115.3 V Fail
Power Factor 0.665 0.669 0.676 0.678 Fail
Final Result Fail Fail Fail Fail Fail

As we suspected, Thermaltake Purepower 500 W can’t deliver its labeled power. Officially this is a 405 W power supply, however when we tried to pull 400 W from it the unit shut down after a few seconds, showing that the manufacturer labeled this unit at 25° C. At least the protections kicked in, preventing the unit from burning.

Efficiency was above 80% when we pulled up to around 285 W from this unit (test number 10), reaching a peak efficiency of 83.5% at 145 W. Curiously when efficiency dropped below 80% (starting on test 11, with the unit delivering 310 W) voltage at +12 V was below the minimum allowed, showing that the unit has already reached its limit, presenting a risk to the components from your system.

On the other hand, ripple and noise levels were always low. During test 14 with the unit delivering 375 W we saw only 22.8 mV at +12VA, 27.4 mV at +12VB, 15.6 mV at 5 V and 15.2 mV at +3.3 V. The limits are 120 mV for +12 V and 50 mV for +5 V and +3.3 V. All values are peak-to-peak.

[nextpage title=”Main Specifications”]

Thermaltake Purepower 500 W power supply specs include:

  • ATX12V 2.2
  • Nominal labeled power: 500 W peak, 405 W continuously.
  • Measured maximum power: 375.4 W at 45.6° C.
  • Labeled efficiency: Above 70% at typical load (i.e., at 50% load – the problem is to know what the manufacturer consider the maximum load)
  • Measured efficiency: Between 75.7% and 83.5% 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: One six-pin connector.
  • SATA Power Connectors: Four in one cable.
  • Peripheral Power Connectors: Eight in two cables.
  • Floppy Disk Drive Power Connectors: Two in two cables.
  • Protections: Over Voltage (OVP), Over Power (OPP) and Short-Circuit (SCP).
  • Warranty: Five years.
  • Real Model: CWT PUF-405
  • More Information: https://www.thermaltakeusa.com
  • Average price in the US*: USD 60.00 (USD 35.00 after mail-in rebate).

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

[nextpage title=”Conclusions”]

To start off, we can’t believe that a company like Thermaltake is still labeling some of their power supplies with a fake wattage. This should be illegal. Officially this unit is a 405 W power supply, however we couldn’t pull 400 W from it for more than a few seconds, meaning that this “official” wattage is also unrealistic, as it was probably measured at 25° C (we test power supplies with a room temperature of at least 45° C and the power supply ability to deliver power drops with temperature).

Being able to get only 375 W from a 500 W power supply is not the worst part: starting at 310 W +12 V outputs were presenting voltages lower than the minimum allowed, offering real risk to your components.

Efficiency was above 80% (peaking 83.5%) when we pulled up to 285 W from it. Coupled with the voltage regulation problem described above, we could clearly see that this unit reached its limits above 310 W and we would recommend the manufacturer to label it as a 300 W product.

Another way to see this is by analyzing efficiency. Usually power supplies reach their maximum efficiency when delivering between 40% and 60% from their maximum wattage. Since this unit achieved its maximum efficiency at 145 W, we can easily say that this unit is in fact a power supply between 240 W and 360 W, confirming our findings described above.

And to make things even worse, this unit is expensive for what it is. For only USD 5 more you can get an OCZ StealthXStream Pro 500 W, which can really deliver 500 W, has modular cabling system and better performance.