I just tried using my $1.99 Logitech Driving Force Wheel for the first time today with GT5 and realized it didn't come with a power supply. Apparently Logitech uses the same AC adapter for Momo & Driving Force wheels as well as the Force 3D sticks. If anyone has a spare one available for sale, I'll buy it. These are the output specs:
24 volts
0.75 amps
center pole positive
edlit: never mind. I just bought one from logitech.com