Anybody know if the Power Mac G5's power supply is pin-compatible (or even pin similar) to any PC power supplies?
The Xserve G5 power supply is totally unlike a PC supply. It's basically just a hefty regulated 12v supply, and the motherboard has onboard regulators for the other voltages. (There's also a seperate regulator in the front panel for the disk drives, that taps the 12v from the motherboard.)
I have no idea about the desktop G5, however.
It's a totally different beast than a PC power supply, or, for that matter, any power supply used in other Apple products.
It's been a while, but I'm pretty sure the Desktop G5's power supply still provides all the common voltages plus 25/28. You could rewire it to fix an ATX conector and it should respond to all the ATX commands.