It is possible to use a PC power supply, however PC PSUs can be dangerous as they easily can pump out 25A or more on the 5V rail - one accidental short in the system and it fries the traces of the computers PCB.
There are ATX breakout boards available on e.g. Ebay or Amazon, which will add fuses to the 12V and 5V lanes of the power supply, so they can be safely used with the CPC and Plus. To avoid any harm to the computer, the 5V fuse should be 4A, the 12V fuse 1A.
[[File:Atx-breakout-psu.jpg|400px]]