I had an old usb harddrive caddy sitting about that only worked with IDE drives. I also had an old usb to ide (both 2.5 and 3.5 drives) and sata drives with no power supply. I also have a variable PSU.
I have a pile of old harddrives that I needed to check the contents of, and rather than buy a fancy usb dock from ebay I decided to recycle my old parts. This is what I ended up with: