charger problems?

I bought a new charger as my Compaq presario cq50 laptop stopped charging about a year ago, since then I have had to buy two more chargers (although I have bought cheaper alternative ones) and now it has stopped charging again. However, I have noticed a slight crack where the lead goes into the laptop. Do you think it is my cheaper chargers not being good enough/overheating/being left on too long or perhaps i.e. short circuit because of the crack?
Thanks :)