Fan controllers just control the amount of volatage (or wattage, I dont remember which, but basically the ammount of power) going to the fan. if it takes some of the power away, the fan only will have enough power to go a certain speed...
as far as making it go faster, they might have somethign on the PCB that can up the voltage (or wattage), sort of like a transformer station for your regular power lines.
Hope that helps a bit.