You're talking about something different. In the early 2000s, before modular PSU cables, Dell used non-standard PSU power connector wiring arrangements. The 20-pin mobo power plug coming out of the PSU was wired differently than the ATX standard at the time, and swapping hardware could fry a motherboard.
Yeah, I wasn't "swapping" PSU cables; the cable was part of the PSU. I replaced a Dell PSU with a standard one, and <smoke!> No more motherboard.
Manufacturers who pull this type of incompatibility shit risk their reputation. I never went near anything with a Dell label again until last year, when I bought a second-hand laptop (I don't attempt laptop upgrades and repairs).