PC ATX supply use and loading

It's discussed in paragraph 3.2.2 of the document I cited. The regulator operates to keep the voltage at 3.3V on the sense line, but that's only going to work if the sense line is connected to the 3.3V supply line.

Sylvia.

That one's no good, try another.

the larger ones have external shunts so you could substitute a different resistor, The 10A one has the shunt exposed on the back, so it could be modded fairly easily too.

you'd have to live with the decimal point being in the wrong place, but I think it's fixed on the ammeter part so that could be cured with a little black tape.

Incorrect; it works just fine in a PC.

It seems to be no good in your application.

I've never had any problem running known good PSUs with no or light loads, but probably not that exact model.