Let me explain in greater detail. Like many Dell products, the 24-pin motherboard connector is wired WEIRD. It is not the standard ATX pinout. The Precision 390 was given to me and did NOT have a power supply. I purchased a used supply for it from eBay, but it will not power on; I'm assuming it's a supply problem.
I do not have any way to measure the voltages on the pins, because you cannot start an ATX supply without having it connected to a motherboard. What's more, even if you could short a pin to start the supply, since Dell scrambled the pins, what pins would they have put that start-up connection on? Dell also scrambled the colors out of their supply. Would I not blow it out by shorting the wrong freaking pins, thank you so much, Dell?
I also purchased a new supply that "supposedly" was made to work with the 390. It's a standard ATX supply with one additional 12-volt plug for the motherboard, but it also doesn't work. The power supply button flashes yellow, indicating that the supply is "nonfunctional." Meaning it's a standard ATX supply, and I am to be condemned to Hell for not buying a brand-new Dell supply at full list price from the manufacturer.
I am hoping that someone who has worked on these (since they were call center standards for years and there must be people who know them) can give me exactly what each pin on the Dell 24 pin cable carries. I can then get a 24-pin ATX extension cable, rewire the wires, and make the thing work. I don't want to move the pins, because I may need a new supply, and I'd rather just plug in a standard ATX supply. There are several of the screwed-up Dell 24-pin charts on the Internet, but none for the Precision 380 or 390. Does anyone have the data? (And no, it's not in any of Dell's own on-line manuals. They want to sell their supplies at full list, and no cheating!)