I fooled with an array (4) 120MM fans on a full H-Bridge motor controller (Pololu brand) and the PWM wouldn't work... Maybe I needed to set the PWM pulse speed lower (less than the 20kHz)? I don't know, but I'd just like a simple way to switch the supply voltage lines without having to rig up a bunch of relays or anything eccentric like that. Maybe a 5-pin relay or something? Mmm... The fans will always be on, so it's not like I need 12V, 5V and Off... They could always run at 12V and be switched to 5V when needed.