It's not that murky.
USB provides two data connections and two power connections.
The data tells the power how much it would like to receive. Which was fine in the old days.
Problem is that the spec. gave a maximum current. So, to get more Amps it needs a fudge. Currently (haha) two plugs covers it.
All true for usb2. Current machine has usb3 ports. I'm using them, but have no idea what they might be able to achieve.