The cord to our original Wii bar was damaged by an unknown culprit, so we went out to buy a new one. All we could find were cordless models, which seemed fine until we discovered how much they eat batteries. So, I endeavored to make it corded, using an AC adapter from my stash, until I realized, "Hey, why not USB?" When it was nearly finished, my daughter said, "Dad, make an Instructable," so here it is. I know that I left out the soldering in wires stuff, but really, it's very easy.
Here we have the victim. It uses 4 AA cells, thus somewhere around or less than 6V. USB is 5V or just a little more, close enough. At least it wont be overpowered. I dug into my stash for a spare cheap USB cable and some other wire and stuff.