PLN means something, but I don't remember what. It used to be FSP had a 530W and 550W power supply that were nearly identicle, except the 530W was 20-pin and the 550W was 24-pin.
If you had a picture it would help. Also, Newegg used to advertise the 24-pin version as dual-CPU compatable without telling you it was 24-pin.
If you got a 24-pin by mistake, it would still be handy for later board upgrades (24-pin power on most new boards). There are the adapters you mentioned, but it may be possible to plug in a 24-pin power supply simply by hanging the extra 4-pins off one side (the holes themselves are shaped so that the power connector only fits in the proper orientation anyway).
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