In a high voltage power supply, why should a resistor and capacitor be wired in parallel with the power-supply rectifier diodes?

In high-voltage power supplies, a single diode rarely has a high enough Peak Inverse Voltage (PIV) rating to withstand the reverse voltage. To solve this, engineers place multiple diodes in series. However, because individual diodes have slightly different internal reverse resistances, the total reverse voltage does not divide evenly among them. To prevent one diode from taking too much voltage and failing, a high-value equalizing resistor is placed in parallel across each diode. This forces the voltage drop across each series diode to be nearly identical, protecting them from individual overvoltage. Additionally, a small capacitor is often placed in parallel with each diode. This capacitor absorbs transient voltage spikes from the AC line or transformer, preventing momentary surges from exceeding the diodes' PIV ratings.