Finally - I would also like to add that this guide shows the CPU unit of what I think is one of the crazy liquid-cooled G5s that made a brief appearance in the Powermac range. The same steps still apply for the more common air-cooled models. The only difference being that my machine's CPU units were secured on their mountings with Allen-key type screws - not Torx screws. Doing this repair was not as difficult as you might think, I managed fine and I'm not a tech specialist.
these Apple support notes are worth a look if you run into problems restarting a machine:
I followed this guide to replace the PSU in my 2x2.0 PCI G5 - it now works great. I'd like to add that my machine didn't boot right away, I needed to reset the SMU on the main Logic board several times and I also re-seated the RAM chips which seemed to cajole the old beast back into life. I replaced a 450W PSU with a 600W and all seems well so far. Many thanks to the team for posting this ifixit guide.