This mod is pretty simple, The Ps3 needs a 12v rail and a 5v rail. The Xbox 360 PSU outputs 5 and 12v (Blue is for the PSUon command, Sending this to 5v will make the PSU turn on-Green light).
For this mod we removed the ps3's faulty internal psu.Step1:
Get a Female xbox 360 psu connector (Off the mobo) and bridge the blue and red and run a wire off it (This will activate the PSU and supply enough 5v watts/amps).
Run 2 wires off the black points (GND), and 1 wire off a yellow point (12v).Step 2:
Connect the 12v wire to the 12v connector on the ps3 mobo, GND to the GND's on the 2 connectors and the 5v to the 5v connections.
(The 5v connector is the 5pin version used on 40gb and 60gb ps3's, 4 pin version may not have the same pinout).
That's all that you have to do for this mod to work, we used a 203w xbox 360 psu and it works fine. The psu fan seems to fun at full rpm, but it is still pretty quiet.