Cool Components™ Four 120MM Fan Kit with Power Supply When two simple fans are needed, say in an SM-SK-RACK-42U, the FK-120-2 are top quality, DC fans with a special levitation bearing system that 'floats' the spindle so there isn't direct contact between the spindle and bearings, resulting in quiet and long lasting operation. Having the advantage of being DC fans, there is more control options for the fans with the variable DC power supply that comes with it.