The following table includes the ripple levels we measured on EDF550AWN’s rails. The limits, according to the ATX specification, are 120mV (+12V) and 50mV (5V, 3.3V and 5VSB).
Ripple suppression was very good on all rails, which was not a surprise to us given the high-quality filtering capacitors that Enermax used in this unit's platform.
The following oscilloscope screenshots illustrate the AC ripple and noise registered on the main rails (+12V, 5V, 3.3V and 5VSB). The bigger the fluctuations on the screen, the bigger the ripple/noise. We set 0.01V/Div (each vertical division/box equals 0.01V) as the standard for all measurements.