Unfortunately the power supply died one week out of warranty. There was a long back and forth with support after one person said they could replace it free of charge since there were symptoms within the warranty period, and another said that person had made a mistake and that I'd need to buy a replacement. Not a good experience and device was out of commission for a long while waiting for their responses. I bought a third party power supply, which I don't really trust, but clearly the 100 USD Microsoft replacement power supply is not reliable either and is twice the price.
Now the power button is becoming unreliable and if it goes I'll be unable to use the device at all as there's no other way to turn it on, and it does reset itself from time to time still. I don't want to move it too much in case it turns off and I can't get it back on again.
I still really like the form factor, but what a review like this doesn't capture is the long-term reliability and service quality that comes with the device, and that's what's most likely to put me off buying another Surface Pro / Surface Book.