This is actually quite common. 3-pin fans will plug directly into a 4-pin motherboard header without any additional adapters. 3-pin fans still have an RPM sensor on them, and most mainboards can ...

I'm trying to change the NMB (Panaflo) fan on my 2 year old Zalman 400W PSU (due to dust). <BR><BR>However PSU surprisingly has a 2 pin fan cable instead of the replacement fan's 3 pin connector.