Here's a quick note. When doing diagnostics and is a possible hardware problem, we don't start with the most obvious thing, we start with the easiest thing. In other words we don't try something that's going to take an hour when there is a less likely issue that only takes 30 seconds. We go for the quick item first so don't waste time spinning an hour on something that was not the problem. From past experience I know there is a problem with laptops that is rare but only takes 30 seconds to isolate. What I have posted below is for that special case where that thing that can be resolved in 30 seconds just might be the thing that is the problem. Most often that's not the problem. But it only takes 30 seconds as opposed to half an hour.Or more! I want you to test and see if the laptop power power brick has a defect.
Run the laptop on battery as a diagnostic, not a cure.
A defective laptop power brick may/will will cause trouble with external devices,modems,routers,printers, monitors and anything the does not tolerable high noise trash. In some cases faulty power bricks pass small amount of power into the laptop common and that passes to extralegal devices.
Just try it. Unplug it. won't take 30 seconds to see.