Not sure I understand here as we talk about non polar electrolytic! An ESR is always measured at a given frequency ? Ohm measurement on an NPE with a cheap will really display a result as the cap is blocking DC ?

Or will you see the NPE ESR through a // precision resistor then calculating the difference between the displayed value and the standalone resitor value?? What is the best precision of a resistor ? 0.001 %, so enough for a lytic ?

Anyway I would like wake uping the np for my understanding.

The serie npe suffering less than the shunted ones in the impedance correction, a gently wake up Elvee suggested maybe will give something near the initial capacitance value permitting a safer new cap purchase (as esr is definitly wasted after 40 years) ?

I have for instance 100 uF npe caps 50 vdc rated in serie as HPF in the passband filter for the mid, measuring 110 uF after 40 years of week-end listening sessions I assume. These ones having no tolerance marking on their bully;;; so it could be initialy a sorted value by the speaker manufacterer between -10% to +20, or + 50%.

Is it o to proceed as this please ? to choose the secondary of a power transformer to feed the npe with 50/60 Hz I assume I have to take the secondary value x circa 1.4 for having the peak voltage ? For illustration 16V secondary is giving almost 23Vac RMS, so near the Vac max of the npe which would be around 35 Vac. How should I close the circuit please ? I take 2 diodes to have a positive drift on a secondary wire, then a resitor in serie, then the serie cap and I shunt towards a further resistor ? (should I have to putt two diodes also on the second wire to have the negative drift took fo gnd reference ? How would I choose the wattage and ohmic values the two resitors ?

Sorry, very noob I am

... non polar cap is strange to me vs polarized

Edit : I also imagine such gadget could be good to burn in tool for any non polar caps, be it film or npe ?