I think you've got a match, thanks for the exhaustive research! I'll add that in addition to the 9 pin D sub connector and the unpopulated switch, the black plastic part right in the center of the back of the board of the camera is a bridge rectifier, which definitely made me suspect a 12VAC input or similar in another design. The lack of controls on the rear of my camera (four missing adjustment pots) and the fact that everything is point to point wired instead of directly mounted to the board point to some kind of retrofit or changing design/parts source. I haven't seen any manufacturer markings on the board itself, but it's clear that there are a lot of options not populated/configured - lots of installed header pins ready for a jumper block, some of which aren't well labeled.
Something to add to your connector topic, though: The "portable" version of the 7290A uses a ~6 contact connector in the same form factor (I replaced it for a barrel jack, and don't remember where I put it....). I got a hold of one with the built in NiCad pack built in (long dead) and it actually used more than four contacts from the power connector, piped them into a board with a relay to switch out the battery when connected to DC power and which held the regulators, but then they just had wires from the board to regulators mounted on the bottom chassis, so the whole inside of the camera was a bit of a bird's nest. It looks like they had a 12VDC input for the camera as well as a higher voltage charging input, at least, all through the power connector in the rear. I pulled the battery, the relay board, and attached some of the stray wires so that it can power up off of just 12VDC like the non-portable variants.