I was curious if anyone has information on repairing a power supply for
a PowerMac G4 733 (Quicksilver). I believe the supply has an issue as it
won't start up the machine, but it spins the fans for a few seconds before
shutting down. Any suggestions or information would be appreciated as the
replacement is quite costly!

Also you could check out:
http://www.repairfaq.org/REPAIR/F_sm...ml#SMPSFAQ_019
but be aware that the capacitors in switchmode supplies can be very
dangerous (as noted in Sam's site). Some SMPSs won't operate properly
unless they're under load, as here in the pdf. (below):
"Note: To verify the power supply, you need a volt meter. When
connecting the volt meter leads to specific pins, make sure the power
supply remains securely plugged into its connector on the logic
board."
I also have the pdf. take apart, troubleshooting and pinouts for the
mirrored door G4. Might be similar.
Richard