@mattblaze You got me interested enough to check a few:
I'll spare you the many failures, but I have two (or three) successes!
"RAVpower PD Pioneer 90W 2 port wall charger" managed to stay on when I plugged my phone into the second port.
Also, an "Anker 615 USB power strip (GaN prime 65W)" did the same. I only checked plugging in a second usb-c plug, not the usb-a. (It is super useful on the road)
And, my PinePower, while not a bit portable, has 5 ports, only 1 usb-c with no disconnections, and helpful voltage displays.
This is a REALLY good question.
I have a similar Anker power strip, guessing it's around the same age too (couple years old?) with a 2x2 port configuration that also behaves similarly. Don't have the model number offhand.
I can also confirm that my "Asometech" 260w giant charger box thing (it's like a pinepower, with more USB-C) seems to behave like a box with four chargers in it: The ports shown in a group renegotiate when things are connected, but the one PD3.1 port appears to be completely unaffected by the lower powered USB-C ports. I didn't have a chance to try the inductive charger. It is, though, also not very portable.
Newer multi-port chargers not only renegotiate every time, but some are extremely slow at it.