Why does AC input have a parallel resistor and capacitor?
The HTCC capacitor is used for filtering and interference suppression of high frequencies as well as the L1/L2 is used for common mode rejection. The resistor is used to discharge a possible load at the HTCC when disconnecting the power supply from main. This HTCC capacitor is also a self-healing type, also typically marked with X2 or Y2 types. They can withstand pulses up to 5 kV.
In the schematics the L1 and L2 should be shown as inductively coupled for common mode rejection, they must be on the same magnetic core.