Why is the power 15W (5V3A)?
In addition to having a plug that can be inserted both forward and backward, the USB Type-C can provide greater power than any previous USB version. Although USB Type-C can support up to 100W of power for USB 3.1 and USB charging, system designers must carefully select features to maintain a reasonable overall cost
The USB Type-C interface uses 15W power, which is six times the standard USB 2.0 charging rate.
For most smartphones and tablets, 15W is sufficient and the cost is reasonable.
Diode rectification and PSR are widely used in adapters with currents below 2A
The normal power of the previous mobile phone power adapter was 5V/2A or lower. Due to its simplicity, optical isolators and programmable benchmarks can be removed, and primary side adjustment (PSR) is often used for AC/DC conversion. Due to the low load current, a diode rectifier was used at this power level. Figure 2 shows a simplified PSR circuit diagram with diode rectification.