Stay away from the guys selling them next to the road ... I have one original Nokia car charger and one "no-name", but from a cellshop .. both work equally well, but I use the Nokia brand, and gave the other one to my wife
Will prolly get the Nokia one if its under R150 here, otherwise a generic from a reputable store. I never get the street vendor stuff! Secondly, you never know if they gonna mug you when you open your window.