I'd suggest rewinding a bit... You're doing the 12v conversion because you're planning on using it in the car? I'm skeptical that a cheap off-brand home DVD player would work well in an automotive environment. Heat would kill it quickly, and it probably wouldn't be very vibration tolerant.

Of course, real in-car DVD players are hella expensive, so I see why you might want to do a hack like that. Good luck and let us know how it goes.