The transformers or those big box things on the plugs get really hot! Try to not leave them plugged in all the time. Also try to keep the heads from breaking off because they are fragile. (the part that plugs into the computer)
The best way to prevent this is to keep the laptop on a desk where it won't get bumped. Every time mine break it was on my bed and my dog would catch the chord on his collar and break it. If you need a suggestion, I think Amazon has the best priced chords. That and Ebay.
Good luck to you.