I don't think that's it, for one thing, my laptop screen is off when docked and it's higher resolution than the monitor the dock is driving. And looking at the task manager the GPU usage is higher now than I've ever seen it, plus the fans are going apeshit

Fun! Now I must insist that you try the other power supply on the dock and report back 😉. It doesn’t make sense to me, but what else would it be? Thermals, somehow?