get a cell phone charger or a drill charger...any type of charger will work that has two split ends to connect. Cut the cell phone charger in half down the middle so you have two wires. Connect those wires to the PC's red and black wires. The fan should work fine..
Note* for more power you must use a higher watt. My PC fan is maxed at about 80w 12v charger. Specs are on the back of a charger.