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

Aluminum 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. Aluminum electrolytic capacitors are polarized capacitors because of their anodization principle. They can only be operated with DC voltage applied with the correct polarity.

Typical applications of aluminum electrolytic capacitors with non-solid electrolytes are

• Input and output decoupling capacitors for smoothing and filtering.
• DC-link capacitors in AC/AC converters for variable-frequency drive and frequency changers
• Correction capacitors for power factor correction