A simple modification I made to use these cheap usb to sata adapter with 3.5 HDDs and DVD readers.
You just need to to take a 12V wall adapter and attach a compatible plug to this thing. Plus goes to the last sata pin (one of the last three to be precise) and ground goes to ground.
Make sure to test it with a DVD drive first, you don't want to lose data in case you shorted some pin.