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As you may gather, most of our kit in the van runs off USB. So our phones, laptop, 4G Access point, GPS watch, fan, Bluetooth speaker, toothbrush, outside light etc etc all need USB to charge. Also, the van and cars have USB powered dashcams.
The problem is., cars only have 12v sockets, and there are a pleather of USB converters from ebay and poundland and other places, but the quality varies. We’ve had cheap ones fail and short out power to a phone causing it to go mental! Also, the newer phones and laptop wants 2.4A, and anything less charging becomes intermittent.
Also, some say they are high powered but can’t deliver the full 2.4A to both ports at the same time, and this has caused us issues. Some have constant “power on” LEDs on them that’s annoying as hell.
We’ve tried loads of cheap ones, and some expensive, but only one works for us – and we have 4x of them in the van (yes, we use that much USB!). the price is right too, in my view surprisingly cheap for what we consider the best – and for sure, don’t pay more! 
They are semi-branded, so at least you have a name rather than generic. they are full 4.8A – so full 2.4A to both USB ports simultaneously, and importantly for us, they are small and flush mount into the socket. (Other 4.8A ones protrude)
So it does what it says on the tin. Not exciting, but buy once, buy right. Don’t end up with a drawer full of cheap attempts! In this instance, you get what you pay for – and we recommend and use these. Don’t just take our word, look on Amazon for 1000+ mostly 4/5* reviews