Which One Needs Replacing?

I'm new to the Mac, so bear with me. I just inherited an old MacBook MC516xx/A. When I plug in the charger, sometimes it works and sometimes it doesn't. So, I'm trying to figure out if replacing the charger will fix my issue (perhaps the charger has gone bad), or if recepticle where I'm plugginig it in on the side of the Mac, is going bad. I don't have an extra charger to test this theory out, so any suggestions would be much appreciated. Is it possible that I'm just in need of a new charger?

Thanks!