The analog 3-pin and MOLEX connectors provide power to the fan to make it spin. Four-pin connectors are digitally controlled and let the system to alter fan speeds dynamically.

It includes the necessary Molex adapter for connecting to your desktop power supply. However, your desktop might not have a drive bay that can accommodate a 2.5-inch drive.

The cable that's supposed to come with the motherboard ends in Molex, but I'd actually prefer Berg as I need to power a CF to IDE adapter that gets powered with a floppy connector.

Would this work? I have two 3-pin fans, each with 4-pin adapters. The adapters aren't like normal psu molex connections though. The two wires going into the molex connector enter via the middle ...

Because Molex specializes in little-notice devices like connectors, antennas and switches, it's also a key Apple supplier. So if you have a smartphone, some Molex products are probably in your pocket.