What is the input / output current and voltage of the charger?
With those factors (input and output voltage current size)
For example, iPhone charger input 100-240v 50-60hz 0.15A max output 5v 1A
China's single-phase AC 220 volts, the frequency of 50 Hz then the charger input power is 220v * 0.15 = 33w output power is 5v * 1A = 5w 33-5 28w power which is the charger energy consumption or input voltage or current
The size of the output power to change that 0.15A behind not also marked a max there is a question is what is the frequency of 50 Hz and what is the role of voltage and current What is the relationship between the charger is hot or charged electrical equipment heat
