Some power supplies will have the primary fan located on different sides, so ensure the rear case mounting screws align. We recommend a single 12v supply >750W ATX power supply that usually exceed +12V@56.25A, but more importantly the +5 standby will exceed +5VSB@2.5A (3A is better for plugging in USB devices into the Pi while in standby mode.) Even an off brand low end Rosewill ARC 750 should work for most machines.