There’s also the possibility they’re referring to the current draw through the mobo connector itself frying things. A couple of HDDs at 12V, 10W will be pulling almost 2A which can be a lot for some circuit board traces, but there’s no great way know what the board can handle without documentation from the manufacturer or someone with relevantt engineering experience well above what a typical computer repair shop would have.

If I were OP I would just roll the dice and try it out. Its not as if old Dell office PCs are high dollar items.