a lot of tow bars just have one electric connector. Caravan tow bars appear to have two.
what's the difference and can a caraVAN BE TOWED BY A ONE CONNECTOR BAR?
Yes. Providing it is the standard connector (and it should be). That one contains the feeds for all the lights at the rear of the caravan. Everything you need to be legal.
The second one (usually has white plugs/sockets) is just 'extras' like a power feed for the caravan fridge.