The diode may break down. If we put a swamping resistor across each diode, the resultant resistance across each diode will be almost the same, and the back voltage will divide almost equally. A good rule of thumb for resistor size is to Multipy the PRV rating of the diode by 500 ohms. For example, a 500-PRV diode should be shunted by 500 x 500, or 250,000. The shift from forward condition to high back resistance does not take place instantly in a silicon diode.
Some diodes take longer than others to develop high back resistance.
The capacitors should be noninductive, ceramic disk, for example, and should be well matched. If T1 and T2 in the above circuit are both 15,000. Output voltage will be 30,000. If T1 is 15K and T2 is 12K the output voltage will be 38,178. If T1 and T2 are both 12K the output voltage will be 33,936.