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5 Power Supplies Get the Full Juice Treatment
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1. Post Stress Test PSUs

Our live stress tests last year served to weed out which PSUs were good for the electronic waste dump and which units merited a closer look. The drop-out rate of 32% also demonstrated that the underlying quality of power supplies isn't as great as many vendors would like us to believe.

The manufacturers of the drop out units went back to the drawing board to make improvements, and sent us new models for consideration. You can read here about how the final version of the CoolerMaster Real Power 550 and the new Hiper Type R fared in our tests, along with information about some new models from other vendors as well.

How We Test Power Supplies

You can read about our test procedures and get the details on our heavy load test platform. Because so many devices dropped out of the running only after a few hours of stress testing, we've also expanded our test portfolio to some extent. In addition to our standard tests, every device must also survive a 12-hour endurance test under maximum load to remain worthy of consideration.

2. Test Candidates In Detail

CoolerMaster Real Power RS-550-ACLY

We included a beta version of the RealPower 550 Watt power supply in our live stress test last year. In those tests, this unit shut down quickly when run under heavy load. The manufacturer investigated these findings and fixed its problems in this final production version. The RealPower 550 model we tested this time around made it through our test regimen without a single glitch.

CoolerMaster even paid attention to our remarks that the unit was pictured upside-down on the retail box. The new unit arrived at our door in a box that showed the unit right side up this time around.

What's unusual about the RealPower power supply is its Total Power Consumption Display, which meters the power consumption of the PSU in real-time. Alas, CoolerMaster has done nothing to improve the display indicator: it's just as hard to read as the earlier model, and its small indicator only imparts its readings at very close range. To us, this makes the display of little practical value or use.

Users can select either a black or silver colored bezel to surround the front-panel display.

CoolerMaster has done nothing to improve the indicator's readability: you can only make it out at very close range.
3. CoolerMaster Real Power RS-550-ACLY, Continued

The new version of this power supply provides two PCI Express (PCIe) power connectors for dual-card SLI or CrossFire configurations. To accommodate this feature, the EPS Workstation connector falls by the wayside in this model, which is probably a good thing because though both plugs are identical the EPS pin-out differs from that for an SLI connector (but that also means this PSU is not suitable workstation use).

The EPS connector had to go, but that makes room for two PCIe connectors for dual graphics card use.

No two-part connector: a plain-vanilla interpretation of the 24-pin ATX12V2.0 motherboard connector.

Those who want to mate this power supply with an older motherboard must use this giant adapter.

Both P4 and P8 connectors are provided, each on its own cable strand.
4. Performance

All the data appears here, but peak amperage values are confusing.

As mentioned above, the new Cooler Master made the scene and withstood our demanding stress test. Even after twelve hours of continuous heavy load, the device didn't shut down: The manufacturer has obviously fixed its problems.

Voltage levels are also stable: The (minus) -12 Volt rail that troubles so many manufacturers, for example, swings only over a relatively modest range from -12.18 to -12.09 volts.

The unit's operating efficiency is also very good. Under light load the unit begins work at a good value of 82.3%; when half-way loaded it runs at about 80% efficiency. It really gets into the swing of things at maximum load: A robust 86.3% efficiency rating catapults this unit to the top of the test field. But under heavy load, the PSU fan really gets going, too: This otherwise quiet device makes an ear-splitting racket when the PSU runs at peak load. At about $110 to $120, the unit's high efficiency ratings never the less justify its relatively high price.

The Cooler Master power supply retail box.
5. Enermax Liberty ELT500AWT

Enermax heads in a new direction with its Liberty series: For the first time, this old-timer among power supply makers offers devices with modular cable management. Enermax doesn't just throw those cables randomly into a power supply box, either: it packs them up very nicely inside a roll-up pouch. This keeps the wiring organized and prevents cables from going astray or getting lost.

This attractive Enermax pouch isn't full of tools...

...instead, it's stuffed with the unit's modular power cables.
6. Enermax Liberty ELT500AWT, Continued

Enermax uses a six-pin connector for its power cables, but it's only possible to switch connectors around in one direction: PCIe cables actually fit in normal device ports, but not the other way around. That means it's conceivable that a graphics card might be supplied with too little voltage and not be able to do its job properly, but this is unlikely to damage any equipment. A different type of connector is used for peripheral wiring, which delivers 5V and 3.3V alongside 12V leads, so that these connections cannot be inserted into a PCIe receptacle by mistake.

An SLI connector fits into an HDD/ODD/Peripheral port, but smaller outlets on the PCIe receptacle prevent HDD/ODD/Peripheral cables from plugging into PCIe ports.

The ATX connector uses a 24-pin configuration in keeping with the new ATX12V2.0 norm, but may be separated into a 20-pin and a four-pin block for use with older 20-pin motherboard sockets. The eight-pin dual-core connector can likewise be divided into two four-pin blocks, so that one of them may be used to accommodate older P4 motherboards if necessary.

Both motherboard and P8 connectors may be separated to accommodate older motherboard configurations.

The Enermax power supply is well made.

The accessories that Enermax includes with this unit show that the company has made a name for itself. However, users must provide their own cable ties (unlike many other PSUs that include cable ties and wire wraps among their offerings).

Users can find the on/off switch and the power cord receptacle on the back side of the Enermax PSU.
7. Performance

As usual for Enermax, the ELT500AWT's device tag tells its story clearly and directly.

As did all of its predecessors from this company, this Enermax device also survived our tests. We encountered no problems during our 12-hour maximum load endurance test, and all voltages stayed within specified levels at all times during testing.

Results from our efficiency measurements, however, were disappointing for the ELT500AWT: it measured only 73.5% at light load, where other competitive products registered over 80% from the get-go. But as load levels increase, so does efficiency: 82.5% is what registers for typical mid-range loads, as one might predict. But we measured only 79.1% under maximum load after 12 hours of testing.

At prices that range from $95 to $100 for this unit, users can buy a solid power supply the value of which is commensurate with its price.

Retail package for the Enermax Liberty ELT500AWT
8. Hiper Type R 580W

This device from Hiper is already well-known to us. In our live stress test, this power supply survived a difficult and demanding 24-hour test. Its only weakness then was its (minus) -12V rail, whose voltages climbed unacceptably high under heavy load conditions. Though this rail is only seldom used in PCs nowadays, and has a high +/- 10% tolerance, we still couldn't countenance taking liberties with the ATX12V2.0 specification. Hiper has subsequently improved this product, and re-submitted this PSU for further testing.

Connector covers keep dust and dirt at bay, and protect the contacts. This replicates standard practice in avionics.

Clever adapter cables save room inside the case.
9. Hiper Type R, Continued

Mix ups are impossible: different types of cables each have different pin-outs.

There is even a standard three-pin connector to report on fan speed inside this PSU.

Cables lock onto the power supply safely and securely.

Though the case includes a tray to keep cables organized and prevent any from going astray, it's a bit large for storing a few unused leads. This attractive plastic box is more likely to wind up at work or on fishing trips, where it can be better put to work.
10. Performance

The Hiper power supply made it through our test regimen without a single hitch. Next, we turned our gaze to the (minus) -12 Volt rail, which caused the device to drop out of our last round of tests. This time we measured it at values of -11.69 Volts under light load and -12.50 Volts at peak load. These values fall well inside the range of ±10% that the specification allows. All the other voltages also fell within allowed tolerances.

To our consternation, the efficiency rating of this power supply worked against its other substantial improvement. At light load, its rating is a paltry 64.4% - the lowest value for any of the power supplies we tested! Increasing the load also increases the efficiency rating to between 76.0% and 76.6%, but this unit wins no prize for efficiency, though these readings are acceptable.

The U.S .version of the power supply does not include Active Power Factor Correction (AFPC) circuitry (though the package may still claim that it does, because it hasn't yet been changed from its European counterpart). At prices that range from $110 to $130, the unit is somewhat costly but is still worth the money for its rated performance and great design.

The Hiper R 580W in what can later be used as a tackle box.
11. Silverstone Zeus ST56ZF

The Silverstone ST56ZF makes a strong impression as a hefty workstation power supply at first glance. This 560 Watt power supply comes in solid, basic black. It's also the only device in our test group that includes a usage indicator: An LED shines green when the input voltage is in standby mode. Once the device is turned on, the LED turns orange. This is a nice feature, and one that's especially useful on passive-cooled power supplies because users can't hear whether the device is turned on or not. But for this reason this feature is superfluous on the ST56ZF: Even under light load, this device can be heard and can become noisy.

The ATX connector comes apart, but the P8 connector (Dual-Core) doesn't...

...that's why you need this adapter

This power supply is equipped with two PCIe connectors for dual graphics rigs

Room to maneuver: the box isn't crammed to bursting like a can of sardines, unlike many other PSUs.
12. Performance

The device tag on the Silverstone ST56ZF doesn't do its own numbers very well (there's no good summary table as on other tags you see elsewhere in this story).

We had no problems with the Silverstone ST56ZF in our testing. It survived our 12-hour endurance test without a whimper. The voltages were very stable across the board, but under heavy load they dip somewhat below nominal values - but even so, they remain within specification tolerances.

The device does earn good marks for efficiency ratings: It measured out at 82.3%, 84.5% and 83.8% for our three load classes (minimal, 50%, peak load). With nearly equal values across the entire load spectrum, this is just what a good PSU is supposed to deliver.

Prices for this unit range from $130 to $140; given its rated performance and high efficiency, we think this is fair.

Retail packaging for the ST56ZF
13. Silverstone Strider ST56F

Silverstone had another power supply to offer: The Silverstone ST56F also offers a rating of 560 Watts, but its design is very different from the ST56ZF. A 120-millimeter fan is the most outstanding among those differences, and makes this unit operate much more quietly. But the Strider also lacks modular cabling.

The back side of the Strider is pretty bare. Next to the on/off switch, and the power cable receptacle, all you can see is a bunch of ventilation holes.

This power supply features separate cables for P4 and Dual-Core (P8) processors.

In keeping with this black power supply, you get black screws to mount it in your case.
14. Performance

This second Silverstone device also earns a "Pass" from our testing efforts. It, too, survived the 12-hour endurance test without complaint, and all our measurements fell within the tolerance established in the ATX12V specification.

The efficiency rating under light load was just about 80% and increased to 83.2% at the higher load levels we tested. Bravo, Silverstone: That's how it's supposed to be!

This power supply will set you back about $130; at that price, it's a good choice.

Retail Packaging for the Silverstone ST65F Strider
15. Performance Measurements

Voltage

This chart shows the total combined power (in Watts) for the power supplies we tested.

Efficiency Ratings

These charts show the efficiency ratings, which represent the relationship between input and output voltage for the power supplies we tested. A perfect efficiency rating would be 1 (or 100%). The higher the value, the less voltage that dissipates as heat from the PSU.

16. Voltage Differences

These charts show the differences in voltage as compared to nominal voltages, measured in millivolts (mV). For these measurements, it makes no difference if these variations are positive or negative. Given a nominal value of 5.0 volts, voltage readings of both 5.01 and 4.99 volts show a difference of 10 mV. The smaller the value, the more closely the value measured matches the nominal value.

17. Voltage Differences, Continued

18. Voltage Differences, Continued

19. Conclusion

The Silverstone ST56ZF Zeus had the highest efficiency rating. With a high efficiency rating that never dips below 83%, it leads the pack, and permits only a small amount of energy to be wasted as heat. But this device suffers from excessive noise; even when only lightly loaded, noise output grates on the ears.

The ST56F Strider from the same manufacturer makes a convincing showing with its quiet operation and also offers high efficiency ratings, though it falls behind at lighter loads. Its price of about $130 is just about right for a PSU in the 560-Watt class.

The Cooler Master Real Power 550 Watt earned the single-highest overall efficiency rating. At 86.3% it outperformed any other power supply we've ever tested in the THG labs. But it dips to 79.9% efficiency at light load, and that cost its maker a first place finish. This device still suffers from a poorly designed power meter, whose small indicator makes it hard to read and only of questionable use and value.

We were pleasantly surprised by manufacturer Hiper: They fixed all their earlier failings from our live test. Today, they offer solid power supplies that follow the specifications and operate without malfunction. They must still improve on their efficiency ratings, however.

Enermax offers its first modular power supply with the ELT500AWT that also comes with power cables nicely packed inside a well-designed roll-up pouch. At a price of under $100, its buyers can take home a solid power supply with an efficiency rating of 82% at medium load (50% of rated power).

If we awarded a prize for design, Hiper would walk away with it hands-down with its Type R power supply. This power supply, with its cable management based on modular avionics-style connectors, will be sure to raise the pulse of any case modder.