Plug-in electrolytic capacitors are composed of polar plates at both ends and an insulating dielectric (including air) in the center. After being energized, the plates are charged to form a voltage (potential difference), but due to the insulating material in the center, the entire
capacitor is non-conductive. However, such a situation is under the condition that the critical voltage (breakdown voltage) of the capacitor is not exceeded. We know that any substance is relatively insulating. When the voltage at both ends of the substance increases to a certain level, the substance can conduct electricity. We call this voltage the breakdown voltage. Plug-in electrolytic capacitors are no exception. After the capacitor is broken down, it is not an insulator.
However, in the middle school stage, such a voltage is not seen in the circuit, so it is all operated below the breakdown voltage and can be regarded as an insulator. However, in an AC circuit, because the direction of the current changes with a certain function of time. The process of charging and discharging the capacitor has time. At this time, a changing electric field is formed between the plates, and this electric field is also a function of changing with time. In practice, current flows between plug-in electrolytic capacitors by way of a field.