The Technical Specifications for my motherboard says that a 20-pin power supply connector can be used with my 24-pin motherboard. What do I give up or lose if I use a 20-pin PSU with a motherboard that has a 24-pin power connector?
You lose the bottom 4 pins, but the voltages are provided on other pins so it is no big deal (unless you have a very high current draw mother board that needs the extra wires.
24-pin ATX12V 2.x power supply connector
(20-pin omits the last four: 11, 12, 23 and 24)ColorSignalPinPinSignalColor
Orange+3.3 V113+3.3 VOrange+3.3 V senseBrownOrange+3.3 V214−12 VBlueBlackGround315GroundBlackRed+5 V416Power onGreenBlackGround517GroundBlackRed+5 V618GroundBlackBlackGround719GroundBlackGreyPower good820ReservedN/CPurple+5 V standby921+5 VRedYellow+12 V1022+5 VRedYellow+12 V1123+5 VRedOrange+3.3 V1224GroundBlack