Ok, this is really embarrassing. The XT60 adapter cable had become completely detached from the stock power supply's connector. When I re-attached it, everything worked perfectly. Nothing to see here. (That connection is buried in an opaque sheath of cables, so I completely forgot it existed.)

Before my UPBv2 mysteriously went dark, I found that some USB 3.0 cables worked perfectly with my ASI6200, and some didn't work at all. If you have other cables laying around, give them a try.

Only thing I know I did was replace Focuser Control Cable #1 (PEG-CMOT-RJ45DB9 to an old Robofocus) with Focuser Control Cable #2 (PEG-CMOT-HSM to a new Starlight HSM). Things seemed to be working, and then, poof (after a reboot of my laptop, I think), none of the USB peripherals are getting power/s...