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 increased current on both +12 V inputs from our load tester to 33 A each (66 A total) and the power supply didn’t shut down. This means that either the OCP circuit is disabled or is configured at a value above 66 A. We don’t like this, especially when the label says the +12 V rail has a 56 A limit.

Under the 66 A configuration described above ripple and noise were too high, above the maximum allowed (at 130 mV). So we decreased current until we were back inside ATX specs (below 120 mV). This happened with the below configuration. Noise level was at 95 mV. See how even on this extreme condition efficiency was still above 80%.