After a couple of rounds of back and forth with tech support, they had me open up the high voltage power supply and inspect for visible damage. Somewhat to my surprise, I found some. These two big black ceramic disks are clearly blown up. By the part number MF72-5D20 these are power NTC thermistors used as surge protection. According to tech support, this type of failure is usually caused by a random power surge.
I have replacement parts on order (they’re cheap) and will try simply swapping out the thermistors as soon as they come in. If that doesn’t solve the problem I will probably have to send the power supply in for repair ($100 plus shipping and handling). Cost-wise, this could have been a lot worse.