Short and sweet with this one - have found these leads in a box and have no idea what they're for: First one looks like it takes a Molex power feed to a fan and then maybe takes a PWM signal from the board to the same fan?? Why the different leads/voltages/whatever? Second one (ignore the screwdriver handle) maybe is a Molex passthrough doing similar to above but with less/different leads? Stumped. The four colours going from one to the other is the passthrough I suppose, but only using the 12(?)v plus white lead to a fan adapter and a single white (what?) lead to a header attachment is something I can't even fathom. I should start labelling these things when I get them.
Its a fan adapter, basically you use it if you motherboard cant supply enough current for the fan (or pump), the 3 pin plug in both cases is for tacho, just in second case they assume that the motherboard is on the same ground as the fan supply and omit the ground wire.
This, it's the kind of think you'd need for your ear bleed inducing delta type fans or the high rpm noctua industrial fans as there's no way you're running one of those off a board header.
Aha! Second lockdown mystery of the day solved, thanks to the bit-crowd! The second lead actually makes more sense to me - straight power passthrough without losing a Molex socket, with a tacho wire attached feeding from the board to the fan. The first lead obviously costs you a Molex socket, but why does it need a ground AND signal lead from the board? I thought if the fan was grounded the board wouldn't need to be (but I know nothing of these dark magicks). Interestingly though, I do have one of those Noctua industrials running in my wind tunnel effort, straight from the motherboard. I haven't gamed in anger yet or adjusted the fan curve in the BIOS properly, so no idea how it holds up but will keep an eye on it.
I've amassed loads of those. I've chucked a few in the bin but I keep finding more - I think they're breeding in the garage.
Tacho only reports fan rpm, so its technically from fan to board + It ensure the fan and board are on the same ground plane In theory it'll be the same, but it never hurts to do it in my experience. Its only 6.6w (if its the 3k one) so you should be fine If it was a 10k or 15k delta then...