The overall concern is watts, which is volts x amps. The higher the volts, the less amps for a given wattage.

Now why do we care if we up the voltage rather than amps? Two reasons:

Too much amps through a wire will burn it out.

Wires have a small but finite resistance. As you push more amps through a resistance the more voltage and ultimately wattage is lost through the resistance.

This is why your stove, oven, AC, electric clothes drier and water heater typically runs on 240v.

So to get more watts to charge the battery with small USB wires, QC and iSmart use higher voltages.

QC uses 5v, 9v, and 12v.

Basing the results you show in your picture, you're delivering 17.8W.

At 5v, you'd be drawing 3.55A for the same amount of watts.