I am attempting to test the electrolytic power supply capacitors in a vintage Forte Model 3 amplifier. There are four, each rated 50v 24,000µF and since they have screw terminals it’s easy to test them out-of-circuit. The LCR meter I borrowed is an East Tester ET4410 (available from, e.g., Amazon). Given the rated values of the capacitors, and since my understanding is that the capacitors function to smooth the 120Hz output from a rectifier, I set the LCR meter to do a series capacitance test, and set the test frequency to 120Hz (instead of the default 1kHz). The test leads from the meter to the capacitor are the four wire Kelvin type. What happens is that the displayed capacitance values slowly oscillate up and down on the meter in a range from about 18,000µF to about 26,000µF. The ESR values also fluctuate between about 2 and 3 ohms. I assume that this has something to do with the capacitor charging and discharging a bit (?). My questions are: why is the oscillation occurring, how can I get a stable (or at least meaningful) measurement result, and is it desirable to obtain the results at the frequency at which the capacitors will operate? Thank you.