Buying a fan controller will give you additional fan headers. Alternatively, you can use 3-pin/4-pin to MOLEX adapters and connect the fans right to the PSU. (MOLEX connectors are keyed as well.) ...

If it isn't an actual Berg socket, then it's probably just a 0.1" pin spacing header. That's convenient, because that's exactly what the Berg pin spacing is, and a Berg connector should plug right ...

We all like to standardise. But there doesn’t appear to be any pin number system defined for one of the most popular wire-to-board connector sets. I’ve always followed the marking used on 0.1” Molex ...

I think they split 'em up that way in case you didn't want to burn out a mobo header if the fan draws too much amperage, by plugging the red/black cable into a molex adapter (4 pin power header ...