340-540V DC under no or extrmely light loads, draw any current from it and it will quickly equalize to the normal VAC expected, especially from a multi stage voltage booster. You want a few amps, I don't think voltage multipliers like this are really a good idea because the ripple currents the capacitors undergo is WAY above what normal capacitors can be expected to give. You're better off using a proper transformer, I doubt any capacitive solution would survive under those loads unless you used something like motor run capacitors, and a single one of those is going to be bigger than the transformer required.