The difference is that Apple didn't even use connectors that *LOOK* like an industry standard. (And, at the time, there was no ATX standard.)
The point is that Dell took an already-established industry standard (ATX) and tweaked it specifically to make it incompatible, so people would have to buy replacements directly from them.
Sony did the same thing, (at least as recently as 2004,) having otherwise-standard ATX motherboards customized to have a different mounting screw layout. (The boards were made by standard companies, like Asus, and otherwise were 100% identical to non-Sony Asus boards. They just had mounting holds different than ATX, so you can't put a "stock" Asus board in a Sony, nor put a Sony-modified Asus board in a standard ATX chassis.)
So, basically what you're saying is that: you avoid using Dell PSUs because they do exactly the same things that Apple did when Apple designed their silly@$$ custom, industry substandard, PSUs for the 68k/PPC era?