I’m surprised this wasn’t a thing until now.
It’s actually amazing (and not something I was aware of so far), but right until now, you could not buy Xbox One power units individually- they either came with the console, or you couldn’t get them at all. This would have been a major issue for quite a few people (for instance, I travel and take my consoles with me to a lot of countries, and differing voltage and current frequencies often lead to my power units blowing up, necessitating replacements), so I am glad something as baffling as this is no longer the case.
From now on, you can get new units at the Xbox Support site; select “Replace an Accessory,” and then choose Power Supply. You can either choose to return a non-functioning power supply to Microsoft and get a new one for $35, or you can buy a new one outright for $50. It’s actually a lot (as far as I am aware, a Wii U power brick, for instance, is only $25), but hey, at least you can get a new one now.