The issue here is NOT an overcurrent condition. It’s undervoltage. The notification is misleading.
I finally got around to put a scope on the barrel jack input and found the cause: Both my microUSB and my barrel jack cable just were too long/low crossection to deliver enough current while staying within voltage spec. As a result, the voltage dropped from 5.17V to just 4.70V at a current of less than 1.0A.
I shortened my cable as much as possible, the voltage now stays >4.9V and the notification seems to be gone for good.
My guess is that the notification is triggered by the Kernel warning “OC ALARM 0x00000001”, which could signify over-current, but more commonly it’s triggered by under-voltage, and some developer just assumed “OC” always means “Over-current”.