Added bonus: It will still work as an Xbox data transfer cable after we are through!
Step 1: Parts List
1. A 12v Switching Power supply capable of 1A.
2. A power plug that fits said power supply
3. A piece of wire (about 3.5" long)
4. An Xbox data transfer cable
5. A full size SATA hard drive
6. A hot glue gun with a stick of glue ready
7. tin snips or pair of heavy duty scissors
8. A little time
9. (optional) patience
I have stressed the word switching as it is very important. A normal "wall wart" is an unregulated voltage source. It will put out the correct voltage ONLY when it has about 50% to 60% of the rated amperage being pulled from it. Output voltage will also fluctuate with the line voltage. For a hard drive this spells disaster. A hard drive needs a REGULATED and CONSTANT voltage.
It's always a good idea to make sure the plug fits the power supply! XO
Now we are going to solder a wire to pins 13, 14, and 15. Make sure the solder hasn't bridged any other pins. Also, make sure to select a wire that can handle 1A of current at 12V. 24 or 26 gauge should be sufficient. Leave enough wire to reach the plug and then add about a half inch.
Then, hold the plug down where you want it, and hot glue it all down!