I wish I could use an external PSU for my desktop!
I'm like you; I want one box / lump, not two (mainly because I move the box around a lot). Consequently, I have a Mac mini. The price cheapest non-used Mac mini however has risen from $500 to $800 in about 3 years.
I'd prefer an external PSU.
I'm at work so I don't have time to do many more googles.
I myself have been building out a brickless skyreach s4 mini system inspired by this [0] (same author as this A300 unboxing)
[0] https://smallformfactor.net/articles/feature/community-featu...
If you integrate the power supply into the inside of the product, then you need to certify the product itself individually once for whatever standard, and potentially for each country you import into.
Hence Apple can do it partly because of a combination of scale and margin, where-as it's a lot harder for smaller manufacturers to do so in a cost effective or reasonable way.
Having said that, I agree with you, external PSUs drive me nuts. And I love products like the Mac Mini that have it integrated.
I bought the Intel version of the DeskMini for $130 a while back. It's about the same price as a normal case + mobo + psu, which it replaces. I put an i5 8400, an M.2 SSD, and some memory in it, and in 5 minutes you have a working system. No hassle, inexpensive, and small. Highly recommended unless you need a GPU.