Ok, right. I agree, Dell has done a LOT of proprietary stuff, but, generally speaking, those systems were FULLY intended to ONLY be used in the manner in which they were set up and with ONLY the hardware they came with. Everything was spec'd for everything else. Adding significantly more demanding hardware to a system using a power brick type power cable, if that's what it is, is a terrible idea. We've seen these kinds of small form factor desktop systems that used laptop style power bricks, that were moderately more capable than those that come with most laptops but nowhere near what a desktop power supply can offer, create serious issues including ruined hardware, fires, fried wiring and everything sideways or in between.
Just because you can get an adapter for something doesn't mean it's wise to use it. It's really no different than the adapters we recommend against all the time that convert molex to six or eight pin PCI power. Or that adapt in other ways. If a power supply (Or whatever) was capable of supporting a given configuration, then 99 times out of 100 it would have come with that connector from the factory. The fact that it didn't tells us it was never intended to be used in that way.
That being said, knowing the full specifications of the power supply for this unit would tell us a lot, regardless of WHAT kind of power supply it is. Knowing a bit of something about the proprietary power convertors on the board itself would also probably be another good thing to know.
Personally, it's not something I'd ever recommend. Any system that can't support a standard PSU of some kind, whether it's TFX, SFF, mATX, ATX or whatever, and doesn't already have the required type and number of PCIe auxiliary connectors that are needed, is a unit that should probably not be used by that hardware in my opinion. I know not everybody is going to agree, but then again, there's a lot of people out there that can't even agree on the most basic, common sense driven things like wearing a mask during a pandemic so it really doesn't surprise me at all that there are always going to be detractors who insist that this or that is "perfectly safe" or that "it's fine". That's my two cents on that anyhow.