Question: what is the difference between 20 and 24 pin power supply?
Answer: You can plug a 20 pin ATX power cable into a motherboard with a 24 pin ATX connector [...] The 24 pin motherboard connector is actually just the 20 pin connector with 4 extra pins added on the end. ... A 20 pin power cable only fits into one end of a 24 pin motherboard connector so you can't insert it incorrectly.