I don't think that the fans will work with just the power supply plugged in and turned on.
It is my guess that the motherboard has some controll over the fans. -- You power up the computer(motherboard) and the motherboard, sensing that it is on, allows the accessories to be powered.
It is my opinion that you should be more concerned with the function of the motherboard, drives, video card, etc. Forget about the fans, they should be the last thing on your "worry about" list.
Lian Li Aluminum Case
Intel D975XBXK2R Mobo
Core 2 Duo E6700 CPU
EVGA 8800 GTS Video Card
Corsair XMS 2 x 1gig RAM
Zalman 9500 CPU cooler