[G4] replacement power supply

[Sara MacLean]

Hi there,
I have a G4 (500 single processor, sawtooth) here that has a power 
supply fan problem.  It sounds like a dying lawn mower & I'm worried 
that my power supply is going to cack.  I'd like to either replace the 
fan or the power supply myself (it's a Delta DPS-200PB-110) but can't 
find a replacement power supply -- apple says it isn't a "user 
replaceable part" but I don't want to shell out the dough for 
installation when I can do it myself.
Any suggestions?
Thanks,
Sara