I'm really not happy that my printer's display "lights-up" when I turn on my connected computer.
This is not how USB is intended to work when connecting one 'machine' to another.
So I had to come up with a fix.
Although USB ports are supposed to provide power for certain peripherals like memory sticks, I don't like it when one device partially powers another.
If I power on my laptop while it is connected to my un-powered 3D printer, the printer's display lights-up, albeit at about half brightness. There isn't enough power for the laptop to fully power the printer, so the printer's controller does not boot.
As there are no circumstances where I want power from one device being shared with the other, the obvious solution was to identify the 5Volt wire in the USB cable and disconnect it.
Its a delicate job cutting through the outer insulation with a Stanley knife, without damaging the inner cores.
But once I'd established (with a voltmeter) that the red wire was in fact 5V (that's not always the case)...
... I cut it and taped up the exposed cores.
Jobs a good un!