Terry wrote:

during charging and waiting periods there is leakage current through the external curcuit this current will accumulate on the cap with the lowest internal leakage driving its voltage up

Sorry, Terry, I highly disagree!

Leakage current is always flowing internally of capacitor. Its motor is the charge sitting on capacitor electrodes. So, if the one electrode has positive charge and the other electrode negative charge, then leakage current will flow from positive electrode to negative electrode, internally of capacitor, through electrolytic material.

Assume, that in transformer solution this leakage current shall flow through the load. How should this work? If leakage current of the most upper capacitor is furtherly flowing through the next capacitor and the next, then this current has finally reached 0V potential of 1200V (400V x 3). But how shall this current flow back to positive side of most upper capacitor? Through the load? Against 1200V? That's impossible! By this trick you could build 'perpetuum mobile'. Leakage current, which can only flow internally of capacitor cannot flow through external load. It's just impossible. The only current which can do this is normal discharging current. And this one will result in a decrease of capacitor voltage!! Why? Because it flows from most positive electrode through the load to most negative electrode and then internally of capacitors from negative terminal to positive terminal and by this resulting in a lowering of stored charge, and by this resulting in a decrease of voltage of capacitors.

Such flow of leakage current, which leads to an increase of voltage of a certain capacitor is NOT possible, because the motor for this does not exist! There does not exist a 1200V source! But only 400V sources which are galvanically isolated!! Because of this, it's not possible to produce by leakage current at any of these capacitors a voltage, which is higher than 400V.

But when this leakage current cannot flow through the load, how will it flow at all?
Very simple: Only internally of each individual capacitor. Leakage current of most upper capacitor, for example, will only flow from the positive electrode to negative electrode of this individual capacitor. Nowhere else! And the motor for this leakage current is the individual 400V winding of transformer, where the capacitor is connetced to. Nothing else!

Kai