Hi so my fans have a 3-1 fan splitter which can be attached to the motherboard, but they also have what I believe to be a 4-pin Molex connector! Do I need to be able to plug both in, or is it more just so people can use one or another?
One or another. Plugging fan into both Molex and fan header (whether using splitter or not) at same time is sure way to get fan killed and possibly motherboard too.