Electric overflow

When I still had a iPhone 4s I used to by all my accessories for it at five below. I did this because they were cheap and worked pretty well. One day I had purchased a charger that had a blue light that would turn on when it was charging. I used it for a few days and then one night when I plugged my phone in it would not charge. I looked at the charger and it was plugged in but the light was not on. When I looked closer I noticed that it had a lot of black dust on the inside. So after smashing it open I found that a resistor inside the charger had over heated and blew up. The whole thing was full of black soot. This relates to physics because we learned that a resistor can over heat and not work anymore. The power exerted from the circuit was too high apparently and therefore left me with a pile of useless plastic.