Where are the plus and minus contacts in the power jack?

My Sidekick II's battery is empty and I'm not sure whether I found the right charger or not.

The charger I found has no printed indication on it's case that it is the original Sidekick II charger. It fits, though, as far as the actual plug is concerned.

But I don't know whether the plus & minus contacts suit the Sidekick II ones.

The charger's plus pole is the inner contact and the charger's minus pole is the outer, visible metal contact.

So would that suit the Sidekick II's power plug contacts? Or will I destroy my Sidekick II because I'll mess with plus & minus here?