The fan should say on the front what the voltage is and how many amps. It's prbably 0.11 - 0.17. You can go to one of these sites and order the correct 12v DC wall adapter, then just run the red to red and black to black.

http://www.goldmine-elec-products.co....asp?dept=1007
http://www.allelectronics.com/matrix...nsformers.html