Only myth is PSUs with single transformer/current source having multiple rails, when marketing says so.
Actually having multiple 12V sources/transformers would be extra cost in components besides making PSUs bigger.
While this schematics is very antiquated in some details, overall structure and functionality is fully valid for basically every PSU:
https://www.smpspowersupply.com/600W_power_supply.jpg
Controller simply monitors 3mV per A voltage drop in R61 and R62 and if voltage drop rises over set limit, shuts down whole PSU.
Only load separation is what length of wires and those current monitoring resistors achieve.
Haven't yet seen PSU with even single filtering capacitor after those resistors.
(and anyway having extra cap in cable near load would be more effective)
Whole mess was cooked up to cover Intel's doings.
Intel's designers referenced earlier standards when making ATX specification.
And one of those standards happened to say you can only output max 240VA (20A @12V) from any single wire/lead.
With that becoming fast inadequate designers invented adding second group of 12V wires with own current limit counted separately.
But instead of PSU makers honestly saying that user has to balance load between leads connected to different limiters, marketing invented BS about multiple rails.
And those earlier standards actually covered also power supplies with higher output power.
For example UL classifies those as Level 6 devices.
That UL Level 6 marking used to be in sticker of many PSUs decade ago.
While having only single high 12V current limit can certainly be considered less safe for HW failure situations/short circuits, safety difference is clearly marginal in normal size PSUs.
After all most quality PSUs used heavily by enthusiasts have been such for dozen+ years.
Though for ~1kW and above PSUs I would certainly consider some current limits sensible.
If max current is 100A, it will get hard to trigger protections by something shorting in end of single 12V wire cable:
Already 0,12 ohm loop resistance would limit current to that preventing PSU from "seeing" short circuit.
But with very high 500+W transients of power hungry cards like RTX 3080, they would certainly need to be fed from multiple current limited circuits, or "fuse" would have be slow, to avoid triggering PSU shutting down.
