The title basically says it all, I have a 20 pin power supply, but my motherboard has a 24 pin port for the power supply. Will the computer still work the same if I just use this, or do I need to find a 24 pin supply?
Not sure how you can claim that PSU is not that old. It's got to be at least 10 years, but I'd have to say closer to 15.
You may have purchased it "new" but it is ancient in computer terms