I have read about people using wall warts as the 5VDC for the Geckos but I believe once word got out that the computer power supply was what was recommended by the designer the practice has faded.
No, I would not use anything other than 5VDC...it does not take much to cook "modern"
electronics..folks have even fried works just measuring them with old VO Meters that used transistor radio (9V) batteries.
This brings up the question....Why not use the computer's power supply? It really is easy to tie into one of the 5V lines; most all power supplies have extra connectors literally hanging around. Just plug a single pin into one of the extra sockets. The color codes for the wires are usually printed on the top of the power supply so you do not have to play plug and hope.
Also the game port has a 5VDC output on pin 1 so you would not even have to open your computer case. The image below shows the pin order.