US DS lite will not charge in UK, only by USB

I bought a US DS lite, tried to charge it with a converter but didnt work. I have been charging it through the USB cable via my laptop and that works fine. I also bought a charger from Ebay (Not a genuine Nintendo charger) but this doesnt work either.

I borrowed my friends Nintendo charger and that charged my Ds up no problem.

Does anybody knoe what i actually need to but so that i can charge my DS up via the mains and not using my laptop all the time.

thanks

mattaus1976