When in doubt, go to Radio Shack. That's the easy solution to finding a variable output device. I have one around here ("multi-output") somewhere for running things from the 12 volt battery in the truck.

There's probably something comparable for in the house. Those various power supply/adapter things come in all sorts of levels. 3 volt, 4.5 volt, 6 volt, 9 volt, 12 volt. I'm just rattling numbers off the top of my head from what I think I saw on the shelf when I was looking at a batch of old transformer things for electric devices.

SRS