just pulled a 470uF, 35V pigtail electro form an old piece of German made audio gear ( Dynacord ).
Behaved initially like it was very leaky, pulling a 16 volt DC rail down to just 2.6 volts.
Tested on a bench supply, with variable current limiting, it behaved exactly like a 2.7 volt zener.
Tested on my trusty Bob parker ESR meter - it read open ( ie more than 100 ohms).
Blasted with 2 amps of DC current - it instantly ceased being a zener and the ESR dropped to around 20 milliohms.
Repeating the above treatments induces event more schizoid behaviours.
This Kraut made cap is plain bonkers .....
.... Phil