I could be wrong fella but I thought the difference was that USB 3 ports are about 10 times faster than USB 2.The S8 would need a decent charge so your issue may have been that your previous USB 2 just didn't have the VA rating sufficient to power your phone. I've had USB adaptors for my old car to plug in the cigarette socket and some would barely charge my S7 phone whilst others would storm it.Like I say, I could be wrong and someone who knows more will be along soon...........
I've got a USB car charger which puts out about 2.4 amps but hardly seems to charge the phone at all. I think my home charger puts out about 5 amps which does the job quickly.
The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire to power connected USB devices.A unit load is defined as 100 mA in USB 2.0, and 150 mA in USB 3.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0; 6 (900 mA) in USB 3.0.
Are you sure about those figures?