I decided to try and make a 12V, 5V, 3.3V DC power supply from the junk box. This is the result. Total cost under $5. I used a large load resistor to pull up the supply voltage and stabilize it. For a little more I could have added a voltage regulator. This one should run 10 amps all day long, max of 20A on 12v, 26A on 5v. That ought to charge your iphone!
