Maximum stable load
We start things off with the maximum stable load, that we measure in steps of 100 watt. The power supply not only has to work flawlessly, it also must not deviate more than 5% on the essential 12 volt-line within the maximum permitted ATX-specification (in other words 0.6V). Of course it is even better if that deviation is as little as possible.
All power supplies achieve the maximum power without deviating from the ATX-specifications, but there is a substantial number of power supplies with an unpleasantly large deviation. Especially if you are planning to overclock, you do not want to see this. The power supply with the smallest deviation is the Bitfenix Whisper 650W Gold, with a deviation of only 0.04V. Four power supplies have a deviation of 0.05V: the Corsair CS650M, RM650x, Enermax Revolution X’t II 650W and the Seasonic Prime 650W Titanium.