What is the purpose of parallel RC network in the bridge rectifier output?
With capacitors in series they theoretically share half the supply voltage between node1 and ground. If that voltage is (say) 100V and you only have 63V rated caps, you can place them in series to get 50V across each cap and prevent each from damage. That's the theory. 

In practice, it is advisable to bias the midpoint at half voltage with the two resistors to overcome differences in leakage currents on each cap offsetting the theoretical midpoint. The resistor values can be quite high but they do need to be significantly smaller in value than either of the equivalent worst-case equivalent leakage resistances of the caps.