Computer power supplies basically only have two tasks: continuously deliver 12, 5 and 3.3 volts to the computer in a stable manner, and preferably do this as quiet as possible. We test power supplies exceptionally thorough. We look at the stability and micro-fluctuations (ripple) of the voltages on the 12V-rails, the efficiency (also at low loads), the stealth consumption and the noise levels. For all measurements we are one of the few test labs that use professional equipment, comparable with what power supply manufacturers would have themselves.
For the tests we use professional Stratron load generators which we used to stress the power supplies in our lab to up to 1600W. Each power supply unit was tested in increments of 100W starting at 200W up to the maximum capacity. At each increment the voltage on various rails was measured. The closer to the official values of 3.3, 5 and 12V the better, while a deviation of more than 5% is unacceptable. We used a professional Zes Zimmer power analyser to measure the power consumed from the power outlet. Based on that we calculated the efficiency. We used an oscilloscope to measure the ripple or the fluctuations of the output direct current.
It is important to know that in all cases we get about 50 watts out of the 3.3 and 5V rails and the rest comes from the 12V rail. This is not the way the 80 Plus organisation and most manufacturers test the power supply units but it is closer to the reality. In a PC the 3.3 and the 5V rails have very limited usage as the power thirsty components (such as the CPU and GPU) only use the 12V rail.
Along with the standard tests we have also tested the units at low loads of 22.5, 50 and 100 watts. These values and the distribution on the 3.3, 5 and 12V rails are based on a real system set up of one Intel Core i7 4770K Haswell-processor, one Gigabyte GA-Z87X-UD3H motherboard, two Corsair Vengeance Pro memory modules, one OCZ Vertex 4 SSD and one CPU-cooler. The 22.5W test comes very close to the idle usage values of the above-mentioned system while the 50W test is based on the situation when one CPU core is functioning fully and the 100W test is based on both the CPU cores being used to the limit.
Furthermore we measured the current drawn by the power supply from the power outlet without any output. It is important to know if the PSU uses up too much power in standby mode.
Our sound tests were conducted in a sound-proof box in order to be able to accurately measure values of as low as 18dB(A). We placed the meter at the distance of 10cm from the unit and measured the noise at 100W, 300W and 500W after the unit has been running each wattage for 20 minutes.