Power supplies are used in all types of digital displays and cathode ray tube (CRT) display.
Any equipment that has electronic circuits in it must have a DC supply voltage available. Since all power in the factory originates as an AC voltage, converters must be used in the power supplies to convert an AC to DC power. The regulated power supplies are typically used with circuits containing linear integrated with circuit elements. The elements of a DC power supply start with Protection devices at the input, including fuses, transient suppressors and line filters then come the transformer to produce the desired voltage from the 220V supply after that, a bridge rectifier and smoothing capacitor is used to produce unregulated DC with ripple.
Also, the filter eliminates the fluctuations in rectifier voltage and produces a relatively smooth DC voltage. Finally, there is a voltage regulator to keep the voltage down to the specified value without ripple.