If the 30amp only draws 1.5 amps at 240v then I could run two of them from my 1Kw genny?
I know Charlie couldn’t run his Ring 50amp smart charger from a 1Kw genny, is the Victron that much lower draw?
for current, rule of thumb is divide by 20
For power, Voltage x Current = Watts. So 50A x 12V = 600W. bear in mind the efficiency side - call it 80% - so that would be around 720W it will pull.
Getting more precise, if it can output 50A at 14.4A say, that would be 720W - throw in the efficiency side and that could be just over 850W potentially at full output on a battery that is around 80% charged (so a fairly specific situation).
I would find it strange that you could't use a 50A charger on a 1kW generator. is it 1kW peak, or constant? What kind of generator is it? If it is not an Inverter-Generator than the output may not be sufficient quality for the charger to work at all and not down to the current output but more the voltage stability or waveform.
I would expect the Victron to be more efficient but not dramatically so.