Equivalent series resistance (ESR) quantifies the non-ideal, resistive losses inside a reactive component like a capacitor. In power supplies, high ESR causes power dissipation in the form of heat and creates unwanted voltage ripple. Technicians often measure this value to identify failing electrolytic capacitors before they completely dry out and rupture.
The capacitance measures fine, but the ESR is over two ohms, so that cap is definitely bad.
A standard multimeter cannot measure ESR; bench techs use a dedicated ESR meter that tests the component using a high-frequency AC signal.
Related terms
Capacitor
A passive two-terminal component that stores electrical energy in an electric field.
Electrolytic capacitor
A polarized capacitor that uses a chemical electrolyte to achieve high capacitance.
Capacitor plague
A widespread issue in older electronics where poor-quality electrolytic capacitors bulged, leaked, and failed prematurely.
Parasitic
An unintended electrical property like capacitance or inductance that exists physically in a circuit.