Most PC fans are powered by 12 volts DC. Check the fan itself - it must say voltage, and current drawn. Go to Amazon, buy a 12 volts power brick with enough current rating to power all three fans, with spare 50% on top (eg, if a single fan draws 200ma, look for 1.5/2.0Amps adapter). Then it is just of proper connecting all the fans, and matching polarity so the fans turn in the right direction.