Is there a positive or negative sign marked on either the connectors or the prongs?
No, but there's a lightning bolt just above the front male prong thing, on the side. Me thinks I need to plug in one thing there. Now for the other one....

Now I can see if my ring thingy is the same as yours and if that solves the problem.
Isn't this fun? LOL! I hope you find the spot for the missing ring thingy.