Id like to make one, and my exhaustive search has not turned up anything that seems to work AND be reliable AND work for a long time.

I tried making one out of a computer power supply, but it will not turn on when wires are shorted across the 5 or 12 v terminals, so, I guess that's out. Id like something that doesnt run off of a battery. Any ideas? I just need the power part, I can build the embedding portion.