Can I use a 20 pin power supply to run a 24 pin mother board?
Jay_nar2012's link is to a thread from 2004 - as such it is a little dated and no longer 100% accurate.
you can purchase a 20-pin to 24-pin adaptor that will give the correct connectivity but you must make sure your PSU has the correct Wattage and Amperage capability to run the board you are using. Bear in mind that a PSU with a 20-pin connector is likely to be old. Check the label on the side of the PSU.