How did Apple know that pd almost succeeded?

The easiest way is to compare the charging speed of your original 5w charger and the original 18w fast charger.

The charging speed of 18w will probably be twice as fast as that of 5w, so you can intuitively know whether it is fast charging.

One more thing, whether the Apple mobile phone is 5w or 18w, there are several processes to charge it.

The first stage, fast charging, reaches 80% of the power.

In the second stage, trickle charging reduces the charging speed, lowers the temperature and protects the battery.

USB-PD is a fast charging specification formulated by USB-IF organization and one of the mainstream fast charging protocols at present. USB-PD fast charging protocol is output by Type-C interface, but it cannot be said that USB-PD fast charging protocol must be supported by Type-C interface.

Common PD chargers in the market all use Type-C as the output interface.

In fact, many mobile phones/notebooks around us have long supported USB-PD fast charging. Starting from 20 17 Apple iPhone 8(Plus) and iPhone X, USB PD fast charging has been supported, but you need to buy USB C-to-lighting data cable yourself. Android camp also supports USB PD fast charging from Huawei Mate 10 and Xiaomi MIX 2s in 20 17 years.

USB-PD fast charging protocol can increase the power transmission through USB cable and connector, expand the power supply capacity of cable bus in USB application, so as to increase the charging voltage or current, and can freely change the power transmission direction.

Type-C interface supports 15W (5V/3A) by default, but after implementing USB-PD protocol, it can support the output power of 100W (20V/5A) at the highest. So now many devices with practical Type-C interfaces will support USB PD protocol.