The voltages are the same - 240volts at 50Hz.
When I'm not roaming with my GP32 (eg. transferring, or trying out new stuff at my PC) I use a Hama Power Supply Card (the german is Stromversorgungskarte) from Maplin. It screws into the place of one of your empty expansion slots (it doesn't touch the motherboard at all) on your PC, and you plug in one of your drive connectors via a splitter. It offers two outputs (as drives run on 12V and 5V). The 5V line is piped straight out the back of your case, and is next to useless. But the 12V line has a jumper set for it and can vary from 3 to 12V.
It comes with eight different power connectors. The smallest of which (and the most useful in this case
) is 0.75x2.4mm. This is the size of adapter you're after.
In the living room, our server powers our network switch at 7.5V. In my bedroom my rig powers my GP32 at 3V. I've cabletied the GP power line to the GP usb cable so I never lose them amongst the cabling hell that is the back of my case (imagine video in and out, mobile phone cables, networking, audio in and out). Bliss!
Of course this isn't much use for playing in the living room, but I've got a PS2, video, telly, and stereo there, so entertainment isn't excatly restricted!
