M6 MR6110 Use supplied power adapter

I had the same issue with a brand new MR6150. Here is what I noted and what I did to get it to work in "Plugged In" mode.

As you have ascertained, the unit does some type of power check on switching to "Plugged In" mode (without the battery). In my case even the supplied Netgear adapter and cable fails this test. After testing 5 different adapter/cable combinations I found that it would pass the test when I used a 20W Apple USB C Adapter with a high quality usb-c cable. The interesting part is that once it  successfully passed the test and configured itself in "Plugged In" mode, it works with any power adapter until you plug the battery back in and it re-configures itself back to "Battery Power" mode once again. I believe this test is only done during the  change from "Battery Power" to "Plugged In" mode. I checked the change over from "Battery Power" to "Plugged In" mode 3 times before concluding it appears pretty consistent.

Once I was able to get it to pass the initial test with the apple adapter I changed back to the supplied adapter and all is well.