What two devices in a computer should be considered "black boxes," and should never be opened due to risks involving charged capacitors?

The two devices in a computer that should be considered "black boxes," and should never be opened due to risks involving charged capacitors are MONITOR and POWER SUPPLY.

Explanation:

Physical contact or close proximity to the open power supply caused a discharge from the capacitor that resulted in an electric shock. Capacitors can discharge current even when not energized because they hold a charge for some time after the power is turned off.To do harm to your body, the voltage across the capacitor's terminals must be high enough to cause a harmful effect on you. There are no hard rules for at what voltage things become harmful, but a common 'rule of thumb' is that DC up to 48 Volt is considered low voltage. So a capacitor charged to a voltage below 48 V is fairly safe.A charged capacitor can be very dangerous, so it's important that you avoid coming into contact with the terminals at all times.