the ADB jacks can handle more than anything you would want to shove in a mac electronics wise, so unless there is a physically broken plug the jack itself is not at fault, maybe some of the electronics

and yes they do make ps/2 adapters, which usually has a small microcontroller translating, if you got a bad one and it fried your board, i would contact the company

If there was a rotten cap in the mix it could have just drawn enough extra current to push it over from rotten to dead