Cooler Master's Real Power Pro 650W
+100W

At first glance, Cooler Master's 650W Real Power Pro looks identical to the 550W model. Both units share a common feature set, including active power factor correction, 80 Plus and SLI certifications, and that handy warning light at the rear. Even their prices are similar, with the 650W model costing about $15 more than the 550W unit.

With 100 additional watts at its disposal, the 650W Real Power Pro is capable of handling 5A more on its 5V line than the 550W model. The 650W unit can also handle an additional 50W of combined 3.3 and 5V power and a whopping 112W of additional 12V power draw.

Not that you'd know by looking at it.

Of course, just because Cooler Master says this 650W model can handle heavier loads than the 550W unit doesn't make it so. Let me illustrate.

If you turn your attention to 12V2—that's 12V power from the PCIe connector—you'll notice it dips to just 10.7V when the PSU is fully loaded. That's nearly a 6% deviation, the biggest drop in voltage we've seen yet. The Real Power Pro's performance is otherwise exemplary. Perhaps Cooler Master's 12V output wattage spec was just a little too optimistic.

Things get even more interesting when we look at ripple voltage. The 12V PCIe line has quite a bit more AC content than the others at 50 and 75% loads, but not because it's exhibiting abnormally high ripple. Instead, the other lines register incredibly low levels of AC content when the PSU isn't fully-loaded. Even at full load, AC content doesn't average out to over 18 millivolts.

The Real Power Pro 650W has no problem maintaining higher than 80% efficiency when loaded to 50 and 75% capacity, but efficiency drops below the 80% mark when the PSU is pushed to its limits. Our calculated 77.5% efficiency at 100% load is actually a little optimistic because the Pro is delivering less voltage than it should on one of its 12V lines.

Update 10/05/2007 — Cooler Master has bumped the warranty coverage of its Real Power Pro power supplies to five years.