Before overloading power supplies we always test first if the over current protection (OCP) circuit is active and at what level it is configured. We configured current on the +12V2 input from our load tester to 1 A and increased current on the +12V2 input to 33 A and the power supply didn’t shut down. This means that either the OCP circuit is disabled or is configured at a value above 33 A. We don’t like this, especially when the label says that each +12V rail has a 17 A limit.

This unit, however, has other protections in action. Below you can see the maximum we could extract from this power supply. Above that, the power supply would shut down. As you can see we could pull up to 545 W from it, being “almost” a 550 W model. But even if we could pull 550 W from it, this wouldn’t make it a 550 W model: manufacturers usually leave a 10-20% safety margin. During this test noise levels where still low (51.6 mV for +12V1, 61.4 mV for +12V2, 19 mV for +5 V and 10.8 mV for +3.3 V). See how efficiency was still above 80%.

The voltage on +12V outputs where, however, at 11.6 V. While this is still inside the 5% margin set by the ATX standard (+12 V output can be between 11.4 V and 12.6 V), it was too close to the lower limit.