Just an FYI, after cutting the Wii sensor bar cable, and attaching it to the back the of wii with the bare wire leads, I pulled 12.04v DC off it. (Red +, Copper - ) So adding in a power adapter not at 12v seems strange to me.
2ndly, I easily extended my wii sensor bar cable over a cat5e+ pre-wired in my walls to home theater system. My equipment is approx 50' away (of cable length, 35' linear) in a back room.I soldered the Wii cable onto a cat5e+ cable, and plugged it into a cat5e jack, which ran over the 50' cable, to another cat5e jack behind my TV. Before I connected it to the sensor bar, I metered the voltage and came up with 12.03v DC. Being this was in range, I soldered the cat5 wire onto the sensor bar wire, and no problems with my WII from ranges of 1' to 10' away.
In short, I'm not sure what people are needing the additional power for. Just my .02 worth.