The fan's molex connections are only two wires (for power) while the RPM line is just a single wire 3-pin connection which is separate altogether. I guess I can just ignore the RPM line in this case.
I've actually got a few of those cables however to connect the 4-pin from the fans to that wire I have to get a couple female-to-female molex wires like here
to be able to correctly connect the fans to the conversion cable pictured above (because the fans have male molex connectors, not female hence the conversion needed). I thought I could get away with just powering the fans from the power supply via the 2 wire 4-pin molex line and controlling speeds from the 1 wire 3-pin RPM line but it doesn't look like I can.