Here's my version of the Mr. Carlson's Lab Capacitance Leakage Tester thingy and a brief demo of it in action. Please don't ask for schematics, as those can be found on Mr. Carlson's Patreon which can be found here:   / mrcarlsonslab  
Also, my assertion that by simply looking at the 5 ma output from the 16V power supply gives an idea of the ESR is totally incorrect! For one thing, it fails to take into account that the LED is drawing current etc.. The actual amount of current the circuit is supplying the capacitor, whilst unknown to me, is probably far less than that which is shown on the meter of the ps. Furthermore, the way in which a proper standalone ESR meter measures ESR involves more than just direct current measurements.