To see what kind of current waveform you get from a computer power supply, scroll down to picture 8 on this page:
http://www.zlan.com/waveforms.htm A rough analogy of how this works is the thermostat in a heating/cooking system. But instead of heat, the power supply is re-filling capacitors. And instead of doing so only when the caps are below a certain level, it just tops them off at a constant rate, e.g. 100 Hz or 120 Hz depending on where in the world you are. The waveform will change depending on how loaded the P/S is.
This waveform really plays hell with a three phase neutral, and also makes voltage drop worse (e.g. heats up wires, CB thermal elements, etc) due to I-squared-R. I'm now doing some investigation into running computers P-P (e.g. on 208 volts) to help mitigate some of this (still inconclusive).
