Operation under Full Load
The full output power of a PSU is the most intuitively comprehensible and, consequently, the most popular parameter among end-users. The PSU label shows the so-called continuous output power. Sometimes, the peak output power is also indicated – the PSU can yield it for no more than one minute. Some unconscientious manufacturers specify either peak or continuous output power at room temperature only. When such a PSU is installed into the real PC, in which the air temperature is certainly higher than the room temperature, the permissible max output power lowers. According to ATX 12V Power Supply Design Guide, the fundamental document on all PSU-related issues, the PSU must operate at the output power indicated on its label up to an air temperature of 50°C. Some manufacturers even mention this temperature explicitly to avoid ambiguities.
Our conditions are relaxed, though. We test the PSU at full load under typical room temperature, i.e. 22-25°C. The PSU works at full load for half an hour at least. If nothing bad happens to it during that time, we consider it as having passed the test.
Our current testbed can fully load PSUs with a specified output power up to 1350W.