I was bored today so I took apart my old power supply and took the fan out. It is a 12 volt unit which low and behold is what the power supply for the system fan slot on my new mobo is. I hooked it up and all seems to be fine. Am I looking for trouble by doing this? Its acting as an exhaust fan and blowing out the air inside my case. It actually sits adjacent to my cpu fan.

Na m8 it will be fine.

PS. I'm assuming that a case fan is simply a power supply cooling fan minus the power supply. I did have to solder a proper connector to the wires which I removed from my old cd rom audio cable connector. A little MacGyvering going on I know.