OCZ StealthXStream 500 W Power Supply Review

[nextpage title=”Introduction”]

After reviewing StealthXStream 400 W and becoming impressed by its performance, we decided to test the 500 W model from this series (OCZ500SXS) to see if it is also a good buy. To our surprise this power supply is manufactured by FSP and not by CWT like the 400 W model, so even though they are in the same series they use different internal designs, making a comparison between the two even more interesting.

The platform used by OCZ StealthXStream 500 W is the same one used by Zalman ZM-360-APS, Zalman ZM460B-APS and SilverStone Strider ST50F, so it will be interesting to compare the reviewed unit to this 460 W unit from Zalman and this 500 W unit from SilverStone to see what are the differences between the three of them. The 600 W model from both OCZ StealthXStream and Zalman ZM series are also manufactured by FSP, but they use a different platform from the reviewed power supply (but the same among them).

Figure 1: OCZ StealthXStream 500 W power supply.

Figure 2: OCZ StealthXStream 500 W power supply.

StealthXStream 500 W is 5 ½” (140 mm) deep, being smaller than the 400 W model, which is 6 19/64” (160 mm) deep. The difference in size is due to the difference on the size of the fan: the 500 W model uses a 120 mm fan while the 400 W model uses a 140 mm fan. Both models feature active PFC, of course.

All cables use nylon sleevings and they all come from inside the power supply, as you can see in Figure 2. The included cables are:

• Main motherboard cable with a 20/24-pin connector.
• One ATX12V cable.
• One cable with one six-pin auxiliary power connector for video cards.
• One SATA power cable with three SATA power connectors.
• One peripheral power cable with two standard peripheral power plugs.
• One peripheral power cable with two standard peripheral power plugs and one floppy disk drive power connector.

Even though the number of cables is o.k. for an entry-level PC, it was a surprise to see the 500 W model carrying less connectors than the 400 W model, which has one more SATA power connector, two more peripheral power plugs and  one more floppy disk drive power plug. Also the video card auxiliary power connector on the 400 W version uses a six/eight-pin plug, while on the 500 W model uses a six-pin plug.

All cables are short, having 15” (38 cm) between the power supply housing and the first connector on the cable. The 400 W version uses longer cables, with 20 7/8” (53 cm) between the power supply housing and the first connector from the cable. On the peripheral power cables there is 5 7/8” (15 cm) between connectors. Most of the wires are 18 AWG, which is the correct gauge to be used, but the video card auxiliary power cable uses 20 AWG wires, which are thinner. Here the 400 W model has the advantage of using wires from the correct gauge.

Figure 3: Cables.

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

[nextpage title=”A Look Inside The StealthXStream 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.

As explained on the introduction, OCZ StealthXStream 500 W, Zalman ZM460B-APS and SilverStone Strider ST50F are based on the same platform and during this review we will be comparing the components used on OCZ StealthXStream 500 W to the ones used on these other two products so we can learn the internal differences between them.

Figure 4: Overall look.

Figure 5: Overall look.

Figure 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.

Even though this power supply has one X capacitor and two Y capacitors more than the minimum required plus one extra coil and one extra X capacitor after the rectification bridge, it doesn’t come with a MOV, which is the component in charge of removing spikes coming from the power grid. This stage from the 400 W model is superior, as it features a MOV.

Figure 7: Transient filtering stage (part 1).

Figure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion about the components used
in the OCZ StealthXStream 500 W.

[nextpage title=”Primary Analysis”]

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

This power supply uses one GBU805 rectifying bridge in its primary, which can deliver up to 8 A at 100° C, if a heatsink is used, which is the case. At 115 V this unit would be able to pull up to 920 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 736 W without burning this component. Of course we are only talking about this component and the real limit will depend on all other components from the power supply. Interesting enough the 400 W model uses a 10 A bridge here, but since on this other model the bridge isn’t attached to a heatsink, its limit drops to 8 A. The bridge used on OCZ500SXS is exactly the same one used on Zalman ZM460-APS and on SilverStone Strider ST50F.

Figure 9: Rectifying bridge.

On the active PFC circuit two SPA20N60C3 power MOSFET transistors are used, each one capable of delivering up to 20.7 A at 25° C or 13.1 A in continuous mode (note the difference temperature makes) or 62.1 A in pulse mode at 25° C, presenting a resistance of 190 mΩ when turned on, a characteristic called RDS(on) – the lower this number the higher efficiency is. These transistors are more powerful than the ones used on the StealthXStream 400 W model (14 A at 25° C or 7.6 A at 100° C) and are exactly the same ones used on Zalman ZM460-APS and SilverStone Strider ST50F.

Figure 10: Active PFC transistors and diode.

The electrolytic capacitor in charge of filtering the output from the active PFC circuit is from CapXon and labeled at 85° C.

In the switching section, two STF21NM50N power MOSFET transistors are used on the traditional two-transistor forward configuration. These transistors can deliver up to 18 A at 25° C or 11 A at 100° C in continuous mode, or up to 72 A at 25° C in pulse mode, presenting an RDS(on) of 190 mΩ. These are the same components used on SilverStone Strider ST50F. Zalman ZM460-APS uses different transistors here, but with similar specs.

Figure 11: Switching transistors.

The primary is controlled by the omnipresent CM6800 PFC/PWM combo controller.

Figure 12: PFC/PWM combo controller.

In summary, the primaries from OCZ StealthXStream 500 W, Zalman ZM460-APS and SilverStone Strider ST50F are identical. Now let’s see the secondary.[nextpage title=”Secondary Analysis”]

This power supply uses six 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 MBR3060CT Schottky rectifiers connected in parallel, each one having a maximum current limit of 30 A (15 A per diode at 105° C, 0.82 V maximum voltage drop). This gives us a maximum theoretical current of 43 A or 514 W for the +12 V output. These are exactly the same components used on Zalman ZM460-APS. SilverStone Strider ST50F uses different rectifiers here, but with exactly same limits. Interesting enough OCZ StealthXStream 400 W uses similar rectifiers on this output.

The +5 V output is produced by two MBR3045N Schottky rectifiers connected in parallel, each one with a maximum current limit of 30 A (15 A per diode at 100° C, 0.65 V voltage drop), giving us a maximum theoretical current of 43 A or 214 W for this line. These are exactly the same components used on Zalman ZM460-APS and SilverStone Strider ST50F. The 400 W model from this series uses only one 30 A rectifier here, thus having a lower current limit.

The +3.3 V output is produced by another two MBR3045N Schottky rectifiers, giving a maximum theoretical current of 43 A or 141 W for the +3.3 V output. These are the same rectifiers used on Zalman ZM460-APS and SilverStone Strider ST50F. The 400 W model from this series uses only one 30 A rectifier here, thus having a lower current limit.

Figure 13: +12 V rectifier, +5 V rectifier and +3.3 V rectifier.

This power supply uses a PS223 monitoring integrated circuit, which is in charge of the power supply protections, supporting OCP (over current protection), OVP (over voltage protection), UVP (under voltage protection) and OTP (over temperature protection, not implemented on this power supply).

Figure 14: Monitoring integrated circuit.

Electrolytic capacitors from the secondary are also from CapXon.

In summary, internally OCZ StealthXStream 500 W, Zalman ZM460-APS and SilverStone Strider ST50F are exactly the same power supply.

[nextpage title=”Power Distribution”]

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

Figure 15: Power supply label.

This power supply uses a dual-rail design distributed like this:

• +12V1 rail (solid yellow wire): Main motherboard connector and video card auxiliary power connector.
• +12V2 rail (yellow with black stripe wire): ATX12V connector, SATA power connectors and peripheral power connectors.

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.

First we tested this power supply with five different load patterns, trying to pull around 20%, 40%, 60%, 80%, and 100% of its labeled maximum capacity (actual percentage used listed under “% Max Load”), watching how the reviewed unit behaved under each load. In the table below we list the load patterns we used and the results for each load.

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.

+12V1 and +12V2 are the two independent +12V inputs from our load tester and during our tests the +12V1 input was connected to both +12V1 rail and +12V2 rails and the +12V2 input was connected to the +12V2 rail.

Input	Test 1	Test 2	Test 3	Test 4	Test 5
+12V1	4 A (48 W)	7 A (84 W)	11 A (132 W)	14.5 A (174 W)	17 A (204 W)
+12V2	3 A (36 W)	7 A (84 W)	10 A (120 W)	14 A (168 W)	17 A (204 W)
+5V	1 A (5 W)	2 A (10 W)	4 A (20 W)	5 A (25 W)	9 A (45 W)
+3.3 V	1 A (3.3 W)	2 A (6.6 W)	4 A (13.2 W)	5 A (16.5 W)	9 A (29.7 W)
+5VSB	1 A (5 W)	1 A (5 W)	1.5 A (7.5 W)	2 A (10 W)	2.5 A (12.5 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	104.2 W	196.6 W	299.3 W	398.3 W	499.2 W
% Max Load	20.8%	39.3%	59.9%	79.7%	99.8%
Room Temp.	45.7° C	45.6° C	45.5° C	45.7° C	48.3° C
PSU Temp.	48.5° C	48.5° C	49.1° C	49.7° C	49.1° C
Voltage Stability	Pass	Pass	Pass	Pass	Pass
Ripple and Noise	Pass	Pass	Pass	Pass	Pass
AC Power	127.3 W	235.6 W	362.2 W	489.3 W	629.0 W
Efficiency	81.9%	83.4%	82.6%	81.4%	79.4%
AC Voltage	109.8 V	109.1 V	107.8 V	107.1 V	106.7 V
Power Factor	0.978	0.99	0.995	0.997	0.998
Final Result	Pass	Pass	Pass	Pass	Pass

With OCZ StealthXStream 500 W we faced an unusual limitation during test number five. With 500 W power supplies we usually pull 18 A from each +12 V input from our load tester and 6 A from +5 V and +3.3 V. However, under this configuration the power supply wouldn’t turn on, showing that over current protection (OCP) was configured at a very tight value. So the configuration for test five is different from the one we traditionally use and we had to pull a little bit more current/power from +5 V and +3.3 V then we’d like to. We also tried to overload this power supply, but we couldn’t: the unit would either not turn on or shut down after a few seconds. Since the goal of our overloading tests is to see the power supply protections working, we must say that they are in place and this unit didn’t burn or explode during our tests.

This unit could really deliver its labeled power at 48° C, which is terrific. Efficiency dropped a tiny little bit below the 80% mark when we pulled 500 W from it. Under other load patterns we saw efficiency varying between 81% and 83%, a satisfactory result that matches this product target audience (entry-level and mainstream users).

Voltage regulation was a highlight from StealthXStream 500 W, with all outputs (except -12 V) always within 3% from their nominal values, i.e., they were closer to their nominal values than required by ATX specification, which allows a tolerance of up to 5% for them.

Ripple and noise levels were always very low. Below you can see the results for test number five. The maximums allowed are 120 mV for +12 V and 50 mV for +5 V and +3.3 V. All values are peak-to-peak.

Figure 16: +12V1 input from our load tester with the power supply delivering 499.2 W (44.6 mV).

Figure 17: +12V2 input from our load tester with the power supply delivering 499.2 W (46.0 mV).

Figure 18: +5 V rail with the power supply delivering 499.2 W (12.0 mV).

Figure 19: +3.3 V rail with the power supply delivering 499.2 W (21.8 mV).

[nextpage title=”Main Specifications”]

OCZ StealthXStream 500 W power supply specs include:

• Nominal labeled power: 500 W.
• Measured maximum power: 499.2 W at 48.3° C.
• Labeled efficiency: 80% at 115 V or 83% at 230 V, both numbers at typical load, i.e., 50% load (80 Plus certified).
• Measured efficiency: Between 79.4% and 83.4% at 115 V (nominal, see complete results for actual voltage).
• Active PFC: Yes.
• Modular Cabling System: No.
• Motherboard Power Connectors: One 20/24-pin connector and one ATX12V connector.
• Video Card Power Connectors: One six-pin connector.
• SATA Power Connectors: Three in one cable.
• Peripheral Power Connectors: Four in two cables.
• Floppy Disk Drive Power Connectors: One.
• Protections: Over voltage (OVP, not tested), over current (OCP, tested and working) and short-circuit (SCP, tested and working).
• Warranty: Three years.
• Real Manufacturer: FSP
• More Information: https://www.ocztechnology.com
• Average price in the US*: 70.00.

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

[nextpage title=”Conclusions”]

In this review we found out that OCZ StealthXStream 500 W is manufactured by FSP, while the 400 W model is manufactured by CWT, thus they use a different project. We also discovered that internally StealthXStream 500 W is identical to Zalman ZM460-APS and SilverStone Strider ST50F.

These other two power supplies are, however, better than StealthXStream 500 W because of the number of cables available. Both feature two six-pin video card power connectors, while OCZ500SXS offers only one. The model from Zalman offers four SATA power plugs and the model from SilverStone offers six, while the reviewed model has only three. And the model from SilverStone offers six peripheral power plugs, while the reviewed model comes with four, the same amount found on Zalman’s.

The performance of the tested unit is good for a mainstream product: main positive voltages closer to their nominal values than necessary, efficiency up to 83% and low noise and ripple levels. It can deliver 500 W, but nothing more than that: during our tests this unit wouldn’t turn on if we tried to pull more than its labeled wattage. Usually manufacturers leave some margin, but this is not the case with the reviewed unit.

OCZ StealthXStream 500 W is not a bad power supply for an entry-level or mainstream PC with one video card, but since it is on the same price range as SilverStone Strider ST50F we recommend this model from SilverStone instead if you are specifically looking for a 500 W power supply.

If you are really looking for a power supply with a better good cost/benefit ratio, we highly recommend the 400 W version of StealthXStream instead. It provides a proportionally better performance at a lower cost. Assuming of course that your system doesn’t need anything greater than 400 W (most mainstream systems won’t) and you won’t need more than one power cable for your video card (you always have the option of converting peripheral power plugs into a video card power connector using an adapter).