My ME-25 now operates only on battery power, following the accidental connection of a Yamaha PSU.
That fact that it's still working at all is a bonus...
Suspecting a blown protection diode, I tried bridging each diode near the power socket with a known-good diode. No luck... I've no idea what's wrong and I reserve SMD surgery for when I am certain of what I'm doing. If it ain't TOTALLY broke, don't attempt to fix it ;)
I will now bodge a second 2.1mm power socket in between the battery pack and the PCB. Crude, yes - but I can't continue on batteries.
I've just blown another one of these. ::)
Same symptom, different cause...
This time, I used an old Roland supply for a keyboard.
It's unregulated and measures 14 volts off-load.
All other devices (Including the ultra-choosy TC Electronic Ditto) work well with it.
???
Down to batteries-only operation, again.
:-[
At least I know what to do to fix it...
Roland AC Adapter Guide
https://www.rolandus.com/assets/press_media_resources/ACAdapterGuide.pdf