My old power supply blew, so I just got a new one. It's p4 plug is unusual--it has not "clip" to secure it to the connector on the motherboard, and will fit in two ways. I'm not sure which way is backwards--I want to avoid toasting my board. Is there a way to tell without the clip? The plug itself is unusual: instead of having two 12v (yellow) wires and two ground (black) wires, it has a 12v (yellow), a ground (black), a 5v (red) and 3.3v (orange). The instruction manual for the power supply (an Antec tp2-550eps) insists this is a standard p4 connector, but does not give instructions as to which direction I should plug it into the motherboard... Google isn't helping. How can I determine which direction is the right direction?

I believe you're looking at the wrong 4-pin plug. What you're describing sounds like the 4-pin main ATX plug that should be plugged in along side the 20-pin plug, to make a 24-pin (20+4) main ATX plug

Hi, Jam is probably right. Look closely at the plug and socket. They usually have a couple of "D" shaped plastic parts that will only go in one way. Good Luck, Jim