“Discharging capacitors is often necessary when working on troubleshooting and repair of electronic equipment. In the old days, tube radios and amplifiers found in every households contained capacitors that continued to hold dangerous levels of charge long after the appliance had been taken off the mains. Then it was CRT televisions, but now that televisions are LED flat screen it looks like everything has turned to low-voltage digital circuitry, so what is the problem? Well, the actual devices may be low-voltage, but the associated power supplies just got from dangerous (tube era B+ supplies) to (relatively) safe (transistorized equipment with linear power supplies) to dangerous again. The culprit today is the switched mode power supply, the efficient and lightweight modern king of power conversion for electronic equipment. A switched mode power supply is based on an input stage that rectifies the mains voltage, yielding a direct voltage of around 330 V (for 230 V mains voltage, 170 V for 120 V mains voltage) for further use by the circuit. Turns out these little nice black boxes that hang from our laptops and are built into practically everything electronic around us that is not running on battery have really some lethal voltages inside.”