This reply doesn't specifically address your query, but your schematic has the load in an odd position. You appear to have half of a Cockcroft-Walton (positive polarity only). It's made up of several Villard cells. (In that sense it's a Villard multiplier rather than half-wave parallel multiplier.) Articles depict the load R1 having the same ground as the power supply.
In that way the bottom row of series capacitors add their charge together, to deliver to the load. Did you try connecting the left terminal of R1 to gnd, and retain its right terminal where it is?