Why is resistor in parallel with capacitor needed in capacitor bank?
A typical DC power supply (like you might find in your phone charger) will look something like this (probably with more protection devices and other extras). The AC will be rectified by a bridge rectifier and smoothed by a capacitor to create high voltage DC. Then a power supply IC will quickly switch the current through a transformer on and off to step down the voltage to say 5V. The output is once again rectified and smoothed, then fed to your phone:







simulate this circuit &ndash; Schematic created using CircuitLab

The resistors across the capacitors (especially R1/C1 because they are at high voltage) are there to discharge the capacitors when the device is unplugged, so that if someone touches the output they won't get shocked. Because the capacitors are there only for smoothing, and not to allow the device to function for a while after power is removed, having the capacitors discharge quickly when the device is unplugged does not hinder their operation and improves safety, so they're included almost everywhere.

Note: I have omitted several things from the schematic, such as a power rail for the converter chip, feedback windings, or flyback configuration, as they do not help to illustrate the functioning of the capacitors and discharge resistors.