Testing – AC Ripple (electrical noise) on DC Outputs
The amount of AC ripple present on the outputs was checked using an oscilloscope. This AC component may be present in the KHz range where most switching power supplies operate or it may be more prevalent at the 60 Hz line frequency. In each case, I adjusted the O-scope time base to look for AC ripple at both low and high frequencies.
30 mV P-P on the +12 VDC output of the Super Silencer 460 watt
The ATX specification for DC output noise/ripple is defined in the ATX12V Power Supply Design Guide.
Ideally we would like to see no AC noise on the DC outputs — the cleaner the better! But in reality there will always be some present. I measured the amplitude of the AC signal (in millivolts, peak-to-peak) to see how well each power supply complied with the ATX standard. The following table lists the ripple/noise results during our 240 w load tests. The four main output voltages of interest (+3.3 V, +5.0 V, +12 V and +5 VSB) were recorded for each power supply after the 24 hr burn-in period.
All three of the Seasonic power supplies exhibited excellent AC ripple suppression on all of the measured outputs. Overall these are some of the cleanest DC outputs I have measured on any PC power supply operating under a moderate load — very good results.