Why does an SMPS use LCR on INPUT?
The yellow thing is an X-capacitor, C11 in the above schematic. The resistor is to discharge said X-capacitor within legal requirements (usually 34 V within 1 second after unplugging), R14 in the schematic. L is an common mode choke, X3 in the schematic. They all form the EMI supression from the power supply to the mains, again within legal requirements.

Please see this old question for more information: X capacitor selection for SMPS power supply