Unfortunately, the Late 2005 Power Mac G5 series uses a custom power supply, as do all Power Mac G5s. To make matters worse, these supplies are rated at 750W to 1kW depending on the model.
Attempting to repair the power supply itself would not be recommended, due to the high voltages involved. Further complicating the matter, removing the power supply from these models requires completely gutting the machine - a very labor intensive prospect, with risk of damaging the processor modules and logic board.
Try to get your local Apple Store or AASP to cover this repair under the REP, if possible.
If not, it is worth having the repair done by Apple or an AASP, as the flat rate labor is a real deal on these units - it takes a competent technician several hours to complete this repair successfully.