This isn't exactly what you asked for, but it is another solution... I have a DC/DC built into my MP3 box. I used one of those remote control car battery connectors for the power plug on it. When in the car, I have it plugged into my battery (duh), and when at home, I use a regular computer power supply and get the 12v off of the hard drive power connector (with remote control car battery connector installed). Works great.