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1 pin is called PS_ON, this shorting to ground turns it on. 1 called PWR_OK which says everything is working in some way I don't want to research. 1 +12V for stand by. 1 +12V sense for detecting voltage drop or something. And then 2 normal +12V and 3 ground. There is 1 reserved pin as well (rectangle connector so needs even pin count)

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> +12V sense for detecting voltage drop or something

This is actually the best bit, incredibly smart idea. It's a kelvin connection to ensure that you get 12V at the motherboard, regardless of power dissipation in the wire.

Why is it important to have absolute accuracy on the 12V pin?

Not absolute accuracy, but you can easily drop a few volts on transmission losses if the cable is poor or damaged.

If you drop a few volts on the 12 V cable of a PC you're about to start a fire.

FWIW, the sense line is for 3.3V, not 12V. The 12V bus will see less drop to begin with, and nobody really cares too much about the voltage tolerance on that one. 3.3V is much more important.

The parent comment is talking about the new specification, which doesn't have 3.3V on the connector.

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