It looks to me that you bought the exact opposite of what you needed. That board looks like it allows you to play System 16 games in a Jamma cabinet, not the other way around.
Normally this kind of mistake will blow the board up, but I think the board should be fine, since the Pandora box doesn't use the -5 rail that the adapter just shot +12 volts over.
Also, the Pandora's box 4 itself is not jamma either. It breaks the standard wiring for buttons 5 and 6, shooting one of them over what is normally a ground.