I've burned up 2 power adaptors!!!

I got a used Mac book pro 15" this past summer. its one of the first ones to that came out I think, and it runs really hot. The battery life is kinda short as well if I'm not plugged in.
Long story short, I have just burned out my second power adaptor!!! The square part of the adaptor was extremely hot when I noticed the light on the adaptor was out and the icon on the screen said,'not charging'. I was using the 3 prong. I burned up a two prong as well last month.

Any idea how or why this happened and what did I do wrong?

Thanks, Ga ntt

Wow that is unusual. Are they always plugged into the same outlet.

If you've burned out two adapters, then I'm also curious to know like Noxian, were they plugged into the same socket?