i dunno a PSU is a little more juice then you'd need to run just a fan, i'm not positive but that could cause more energy to be put into the fan then the motor is capable of handling....

you don't have any old A/C adapters (http://www.bizsyscon.com/pics/AC_ADAPTER.jpg) lying around anywhere?

what could also work (you might wanna get this confirmed i'm not positive) is just cutting the plug off some old appliance... (old clock, vcr, anything tha tplugs into a wall outlet that you don't need) and wire it that way.... the only thing that throws me off is it saying 120 Volt AC... but it does show a standard wall outlet plug in the picutre (not an ac adapter)