An aluminium electrolytic capacitor, often only called an electrolytic capacitor, uses aluminium metal as one electrode, covered with a very thin layer of aluminium oxide as dielectric, and which has an
the electrolyte as its second electrode.

Aluminium electrolytic capacitors are typically used in power supplies and DC-DC converters for smoothing and buffering rectified DC voltages in many electronic devices. They are also used in industrial power supplies. Aluminium electrolytic capacitors are polarized capacitors because of their
anodization principle. They can only be operated with DC voltage applied with the correct polarity.