**There are 2 pins on 4Pin Case Fan socket connection side. (the third pin is for fan speed monitor, which only use in motherboard fan header)
It can connect with 3Pin or 4Pin case fan.
Not enough fan sockets on main board? No problem! Get this adapter and you can connect your 3-pin fan directly to your PSU.
The product comes with only 2-pins for the power as shown in the figure above but it will work for 3-pins fans.
Now with this conversion cable, you can bring as many fans into your PC case as you like.