The general usb data cable has four lines, there are two data two power sources, the default charge into the phone is 5v, if the phone supports fast charge in the low power when the two data lines will have a voltage of a few tenpoints of volts from the phone feedback to the charging treasure to the charging treasure detection, belongs to a protocol, the general explanation is that 'I have too little power your 5v charge is too slow, give some force', So the charging treasure knows that the voltage will jump from 5v to 9v or 12v to charge faster, and when it is full, there will be another feedback voltage that is different from the previous voltage to the charging treasure to let the charging treasure know that the phone is full, it will jump back. Fast charging is a protocol, common qc fast charging Huawei fast charging pd fast charging and so on, some are compatible and some are not compatible, these are a different matter. However, almost all of the principle of fast charging is from the data line feedback to the charger a signal so that they communicate with each other.