It expects to be powered using the molex plugs, and drive a number of fans through the fan headers. I'm pretty certain it'll work the other way around , i.e. you could connect 5V to one header, 12V to another, and runs fans from that. It's not a terribly complicated device.
There was some debate a while back as to whether these things would damage a power supply, but as far as I know nothing came of it. If you 7V fan mod you'll find the diy way to do the thing you've linked in the OP.