This cable is 5V USB port to small 3-pin / 4-pin fan cable, it allows you to power most case fans by using a USB connection, 3pin or 4pin case fan power adapter cable both OK Connector: One is USB port, another one is small 3 pin / 4 pin case fan power adapter cable port Cable length: 11.8inch Fan must have a start voltage at or below 5V (fans with a higher start voltage will NOT work) 12V fans will be operated at a reduced 5V voltage for silent operation