Step 1 - add up all of your modules' current draws, then increase that by 1/4th. That additional draw amount is there to deal with inrush current, which is what you get for the first fractions of a second when the rig is turned on. If the final amperage figure there exceeds the current ratings of the P/S, then you've probably found your problem, and you'll need to replace the Arturia supply with something beefier. If not, then...
Step 2 - After acquring a new supply, remove ALL modules from the rig, then take some canned air and blow out all of the headers on the distro. If there's a bit of wire or something else conductive in there, this should remove it. Shrouded headers are very convenient, they tend to prevent mispolarized connections or connecting a ribbon a step or two off from its proper alignment, but they can hide bits of crap...and if one of those is shorting something, that dead-short will do that. Once this is done, turn on the rig with only one module connected. If the supply blows again, the problem will be a defective busboard. If not, then...
Step 3 - Start adding modules one by one, checking power integrity each time you add a module. And before each time you do this, remove the ribbon from the module and visually check each ribbon beforehand to make sure there are no nicks in the insulation, no shorted-looking bits around the connectors, and especially nothing that looks burnt...as there's enough amperage there to melt insulation if there's a short. Having done this, then blow out the power connection on the module (AWAY FROM THE OPEN MODULAR! You don't want to blow something into the cab to start the whole mess all over again!), then replace the ribbon and connect the module to the busboard. Turn on. If nothing happens each time, then WIN!...you probably had something in a module header. But if the P/S blows up yet again after reinstalling a module, the fault is with that module and now you know who to contact about their defective product.
Yes, this sounds like a kludgy way of troubleshooting a power issue. But the fact is that a typical Eurorack contains so much that's going on on the inside that, without a test module (such as Synthrotek's TST or vpme.de's p0wr) that lets you check module functionality, this is about the only systematic way to do this. Annoying, yes...but it comes with the territory. One other suggestion would be to invest in a cheap multimeter. With that, you could check the busboard to see if there's any continuity between the "hot" rails and ground (WITH THE POWER SUPPLY REMOVED AND RIG OFF!!!). If you see continuity between those, then something's wrong as those rails should only connect through the components connected to them. And while the Arturia Rackbrute distro does have filtering, none of that should be a problem as long as you check for continuity in BOTH polarity directions; if you see what seems to be a short, then reverse the polarity of the multimeter probes...and if this persists, then it IS a short. If not...then no, you're just getting continuity through a polarized component, and reversing the direction of current causes the polarized component to block the multimeter's DC. That's what you want to see.
Which brings up another point that needs to be mentioned: modular synthesizers are NOT entry-grade technology. Not even close. While this all seems like plug-n-play stuff, really, it's not...and there's a certain level of technical capability that anyone considering getting into modular synths needs to have before spending that first dime on a new rig. Having a multimeter and knowing how to use it is important. Basic skills with electronics tools such as soldering irons and wire strippers...those come in handy more than you'd think, if just to repair patchcables. Understanding how to logically troubleshoot by elimination (what's going on above in this post) is an essential. And a good appreciation of what an amp or two of "low-voltage" DC is capable of is another essential...which, frankly, you don't want to obtain first-hand.
