NOTE: THIS PROJECT REQUIRED MESSING WITH HIGH AMPERAGE ELECTRICITY, AND THE DANGER OF FIRE IS HIGH! DO NOT ATTEMPT!!! (Unless you absolutely know what you are doing.)
I have a modified UM2 (olsson, Meduza/Rober feeder, 1.75mm conversion) which has been working well for about 4 years.

A month or so ago, my power supply just stopped working, 0V, no blue light. The printer still worked if I plugged my UM3 PSU in.

I needed to keep printing, and I happened to have a high amp 24V PSU that I'd been saving for a CNC project. After opening the brick and determining that there was nothing I could fix, I removed the output wires/cable, soldered some leads to the end and connected to my power supply.

Mostly because the replacement is pretty expensive, and the new supply was working, I decided not to order a new one.

the only downsides were that the new powersupply wasn't very portable, and was very loud (it has a fan)

During this, @gr5 told me that these supplies sometimes they come back to life when you let them sit over night. Sure enough I plugged the brick back in and it was working again. I didn't trust it enough to reverse my "borrowing" of the cord so I came up with a different solution: install a female barrel jack in the brick, and also on the new power supply. Putting a plug on the cord, I could swap back and forth as I see fit. I designed the adapter in Autodesk Fusion360 (it was pretty simple)