1.1 What is power supply at all?
Power supply is ... , in a bold definition,
"an equipment that converts in some way inputted electric energy
Figure 1.1 Power supply equipment
For example, AC to DC, DC to AC, 100V to 50V,
rotational energy to electric energy, or single voltage to multiple
voltages, and so on.
Figure 1.2 Conversion by power supply equipment