As I recall, you're interested in a railgun or coil gun. The massive magnetic fields these things kick up could be a problem for fancy power electronics, so I suggest you go old school and follow mk_'s solution: a step up transformer and diode rectifier.
I also recommend using an isolating transformer so that one rail of the cap bank (typically -ve side) can be connected to earth. That way you'll know if you've got an accidental earth connection (and by 'know' I mean 'thank goodness we're wearing earmuffs and safety goggles).
To get 400V DC output, you need 280V RMS. I suggest the following setup:
230V input -> big ass series resistor -> single phase variac -> 230 : 280V isolating transformer -> diode rectifier.
The variac isn't strictly necessary, but it will help you control the final charge voltage of the capacitor bank to achieve consistent results. Please note that variacs are almost never isolated!
Now, an interesting trick you can use here is to deploy a non-linear resistor so that it doesn't take forever for the last bit of charging. A couple of 500W halogen floodlights can be very effective in this role (just make sure they're not too close to flammable stuff as the beam out a lot of infra red). When their filaments are hot, their resistance will be around 100 Ohms each, thus limiting peak current draw. When their filaments are cold, their resistance will be along the lines of 5 - 10 Ohms each, which will help get the last few volts into the cap bank without waiting for ages.
Yes, that is correct, Railgun however I have tested both, Noted for the halogen light, the large element I used has the exact same effect (if it didn't I'd probably want to contact a physicist or write my own paper on it, as that would be breaking the laws of physics hehe), although not as much, it gets to a few hundred degrees, and then kinda stays there, even after charging is done (that poor bridge rectifier, I bed I'd fail if I left it on like that)
Note the gun will feature 4 stages, as in electrical safeties.
Safe (no charge, mains off, all contacts bridged),
Primed (charging, charge supply connected, or charged and charge supply connected) ,
armed (charged and charging supply disconnected, all contactors open except rail ones [Oh boy, I might make these ones out of copper myself for current]) and
firing (SCR's activated, capacitors hopefully still alive, as would the SCRs and back EM protection). This is the main reason I'd want to construct my own supply, as to ensure this system won't randomly fire a hunk of steel into my chest or something else bad.
I will probably use the transformer method with 240 (Ireland still hasn't moved to the EU's 230v) to 280 (sweet, my maths was only about 10 volts off) and rectify that, I prefer simpler circuits, however there will be filtering even before the transformer, common mode chokes, MOV's and maybe not suppression capacitors, but if I feel they wouldn't hurt I have bags of them. I'll have a look to decide whether toriodal (I'm a big fan of them, I just like them) or a more standard will be used, however I might go with a standard one as they're easier to work with.
The gun's negative rail will indeed be tied to mains earth, and the positives rail by some 2KV capacitors, hopefully that also helps quell some magnetics. I might also use a plasma armature and not use SCR at all, instead fire a high voltage pulse to generate plasma and hope that dumps the power, but that would definitely destroy the rails faster, as it stands titanium was a massive sparkly failure (pretty to watch though). Also the miss alignment of the projectile becomes a factor, so it depends on small scale experiments.
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