As MannMann has already written, they are 3-pin fans. I replaced mine with the following Corsair SP120 Quiet Edition High Static Pressure, 2-pack (120mm).

Both fans have a 3-pin connection and can therefore only be regulated via the voltage. To be honest, the fans were not quiet enough even when regulated down and had to be replaced quickly.

However, I would rather describe myself as a silent fetishist.

I'm not 100% sure anymore, but I think they were only 3-pin fans, unfortunately.