Final answer:
A capacitor is the device that can retain a high-voltage charge after power has been removed, due to its ability to store electrical energy between two conducting plates separated by an insulator.
Step-by-step explanation:
The device that can retain a high-voltage charge after power has been removed is a capacitor. Capacitors are specifically designed to store and retain electrical energy in the form of an electric charge. They consist of two conducting plates separated by an insulator (dielectric), and when connected to a battery, they accumulate equal amounts of positive and negative charge on their plates. Capacitors have a variety of applications, from filtering noise in radio communications to storing energy in medical devices like heart defibrillators.
Other components like resistors, inductors, and diodes have different functions. Resistors dissipate power as heat, inductors store energy in a magnetic field while current is flowing, and diodes allow current to flow in one direction only. However, it is the capacitor that is capable of holding a charge even when disconnected from the power source. This ability to retain a charge can present a shock hazard in high-voltage circuits even when the device is off, requiring the use of a "bleeder resistor" across the capacitor to safely discharge the stored energy.