Work cycle is entering AC Current power supply 220Volt the transformer T1 will convert AC to lower left 9V will be switched from AC power into DC with D1-D4 connected to circuit Rex Comment fire Bridge Terminal. (Bridge-Regtifier) will be Current Filter to smooth further the capacitor C1, which at this point can be used as Vout by’ll volt approximately 12Volt the output level one will be diode D5 acts to prevent AC voltage. through the connection of the output level will be a DC current flowing into pin 1 of IC1 by IC1 acts as the regulated voltage to 5 volts out in three legs of IC1, the output level.
The second capacitor C2 and C3 is a current filter to smooth more.