Samsung Galaxy car charger

I bought an adaptor to convert the cigarette lighter into a USB socket. I
thought this would allow me to power my Samsung Galaxy Ace whilst I was
driving, which is essential considering how Satnav, music apps will zap
the already poor battery life.

But after plugging it in, the light comes on on the adaptor but the phone
doesn't start charging. It's possible that either the adaptor is faulty
or my car doesn't provide enough power to charge the phone. I could
purchase a lead specifically designed for my phone, but before I do that
has anyone had success getting this model of phone to charge in a car?