for 3 pin fan pinouthttp://pinouts.ru/Slots/USB_pinout.shtml
for usb pinout.
the voltages are different, 5v vs 12v but it should still spin the fan but about half speed. connect 5v to 12v, ground to ground. get some small butt splice crimps and then can heat shrink tube it to look nice. put tubing on before crimping:)