USB charging - an end to a nightmare

One of the things that has caused me more bouts of pure RAGE over the last year has been keeping things charged on the move.
When the mobile phone makers finally, after so many years of selfishness and greed, to standardize on one charger there was dancing in the streets. Finally you would be able to borrow someone's charger if you had left yours at home. And charging from car power points might finally work.
Being me, of course, the one exception was my Motorola Defy, which proved to be amazingly picky about what it would accept a belt of electricity from. The mains, yes. Battery-powered charging packs, no. My car...no, no, no.
I understand that many Android phones have the same problem.
It is particularly irritating in the case of my Defy because its splashproof ruggedness makes it my preferred phone for boating and camping, exactly the time when I often can't get to the mains.
But the other day Carphone Warehouse (bless them) popped a Zagg dual-USB car charger in the goody bag of an event I went to, so I thought I would try it on the recalcitrant Moto, without, I have to say, very high hopes of success.
And it worked! The Defy actually deigned to take a charge from the car!
How it is different from the standard USB car charger I don't know, but the Zagg is now plugged permanently in my car's power socket.