If this is just to power the nixie tubes, then the current required is pretty low. You would probably manage it with a mains transformer used backwards, running off the logic supply transeformer : Suppose the logic supply transformer has a 9V secondary. Get another, smaller power, mains-to-9V transformer (say use 50VA for the first one, 20VA for the second, those are likely to be overkill). Connect the 'secondary') of the second, smaller, transformer to the secondary of the first one (which still supplies the logic PSU circuit). That second transformer will acts aas a step-up transformer, and will give you something a bit less than mains voltage across what was originally its primary winding. And of course that's totally isolated from the mains. If you manage to get a transformer designed for 230V mains for the second one (or one with 2 115V 'primaries' that you can connect in series), then just rectiying it would probably be OK for the nixie tube supply. If you can only get one with a single 115V primary, you could use a voltage doubled rectifier. Either way you'll end up with something over 300V DC -tony