As you could see from the above picture, in terms of power output, QC 3.0 is not much different from QC 2.0 to be frank, however, they are not the same in these ways;
QC 2.0 multi-voltage is fixed at 5, 9, 12 and 20V. This fixed voltage means the charging is done in voltage stages.
QC 3.0 can change exact voltage and can be anywhere between 3.7 and 20v, the charging is variable and this increases the overall efficiency of the charge.
QC 2.0 jumps in stages, less efficient but still enhances speed.
Standard fast charge stays at 5V and provides a slower charge.
The advantage of QC 3.0 is that it can provide optimal voltage at the precise need of the battery, so during charging you are always at the fastest charging voltage. Simply, we can put it this way;
3.0 IS SMARTER
THE VARIABLE VOLTAGE DELIVERS FASTER CHARGE WITH THE SAME POWER.;
C. AND, PEOPLE ARE TALKING ABOUT QC4.0, WHAT'S NEW WITH IT?
First of all, please see the picture below which shows the evolution of Quick Charge from 1.0 to 4.0;