It varies a lot. Many of the external drives use an external power brick that connects to the drive using a 6 pin mini-din cable (like a ps/2 keyboard cable but with six pins). In the enclose I had two pins are ground, two pins are 12v and 2 pins are 5v. I wired a cable to connect a molex connector to the appropriate pins. Infortunately I wired it wrong and fried the hard drive in the enclosure. So, go very careful.Originally Posted by Kato
If you can find one with a regular single voltage barrel connector then you can get a radioshack dc-dc adapter to run it on.