What hazard exists in a power supply immediately after turning it off?

Power supplies often use large filter capacitors to smooth out the converted DC voltage. These capacitors act like temporary batteries and can hold a substantial electrical charge even after the device is disconnected from the main power source. If a technician touches the circuit immediately after turning the unit off, these capacitors can discharge through their body, delivering a dangerous or even lethal shock. Good power supply designs include "bleeder resistors" to safely drain this charge, but these can fail, so extreme caution is always required before touching internal components.