> But literally every device in the real-world just wires the port to the 5V rail with 2 A overcurrent protection
Except Macs, Macbooks, iMacs, I think also at least the Thunderbolt Display from <very many years ago>. They all have a software overcurrent protection that is very triggerhappy. No negotiation and it will whine and shut the offending device off, and same if the negotiated current draw is exceeded.
Might be worth a try somewhen when I'm rich enough to afford a dynamic resistor bank to verify all the characteristics...
I've never had any issues running dumb USB loads off any of my MacBooks. Just tested it, no problem running 1.7 A of dumb resistors just soldered to the power pins with nothing on the data pins at all (not even the passive "apple charging" resistors) https://kalleboo.com/linked/usb-dummy-load.jpg
Macs will shut down a port if it goes over 2.4 A (IIRC) without USB-PD negotiation (mainly with the cable rather than the device).
But the USB standard says they should limit to 100 mA without USB 1.x negotiation, and it's not doing that.
Except Macs, Macbooks, iMacs, I think also at least the Thunderbolt Display from <very many years ago>. They all have a software overcurrent protection that is very triggerhappy. No negotiation and it will whine and shut the offending device off, and same if the negotiated current draw is exceeded.
Might be worth a try somewhen when I'm rich enough to afford a dynamic resistor bank to verify all the characteristics...