If you have one of these lying around you don't need,let me know and how much,
jmlachance@hotmail.com
If your 400 is the Sawtooth model (PCI graphics) then the power supply from a G3 B&W PowerMac should work. I happen to have one :)
Apple part # 614-0085.
You can have the complete, working (except for bad optical drive) tower for $35. Or $20 if I keep the memory, processor, disk, and video card.