Glowforge doesn’t sell the power supplies so you’ll most likely need to ship your Glowforge back for repair (if they’re currently offering option) or to swap it with a refurbished Glowforge (much more likely). Either way you’ll need to contact support and it going to be expensive.
The only way to get a power supply on its own is to buy a used one from someone who’s parting out a dead machine. But be warned that the power supply is not easy to swap out. According to discussions I’ve seen on the openglow forum it’s very difficult to get the high voltage cables connected and disconnected, as they snake through the machine in a very inaccessible path.