Howdy!
I've got an 857d, and the connector on the radio side of my power plug had a similar issue; turns out that the metal pins inside the plastic connector weren't fully seated because they'd worn into the plastic and didn't allow for a solid connection.?
I cut the 'molex' connector off, installed an Anderson Power Pole connector using the ARES standard, and haven't had any issues with power connections since.
I've also been using APP connectors for more than a decade on various other DC powered equipment in my vehicle, office, and shop without any issues.
If you want to go the 'long route', you could check/verify the issue is the pins in the power connector (again, radio side, not the power connector side that connects to other radios fine), and just replace the external section of the molex plug. If you do this, i'd urge you to spend the money to buy the better quality one so you don't have this issue again.
73, de KI4WIN
Daniel