I'm familiar with the IIcx/IIci/Quadra 700 issues. I have at least one machine that exhibits such problems myself and, though I haven't taken the time to work on it, I've found that the power strip workaround is acceptable.

It's definitely not a motherboard problem. I've already isolated it specifically to the power supply itself.

Is the problem with the IIsi the same as that exhibited in the IIcx/IIci/Quadra 700 Macs? It's not the same power supply, and the IIsi is a unique form factor, but I suppose the symptoms are similar. Does anyone have a schematic or something for the IIsi PSU?