The following info was told to me
back in the 80's. I don't know if it is true, I flew American equipment until the mid-80's. Maybe someone on here would care to correct me if I am wrong or add to it if it is all true...

Back in the old days, the importers of Futaba (in California?) wanted their stuff to be different than Airtronics. (JR was practically non-existent at that time) So, Futaba went negative shift in North American market. Airtronics/JR stayed like they were, Positive shift.

Now something different...

In a similar way, JR had the first charge jack of the current size and shape. They chose negative center pin polarity for some odd reason, I guess it had to do with the close proximity of a circuit board with + on the edge or something.

I can perfectly understand why Futaba went with center pin negative (I would have), but why they would choose the exact some size charge jack? I have no idea. They sure caused problems for everybody.

Negative-center-pin polarity is not totally unusual to JR. Ever bought one of those universal power adapters at WallMart or Radio Shack? On similar connections they allow for polarity changing for compatibility with different applications. I have an old adding machine that uses the same polarity, center-pin-negative, different voltage though.