cases have power supplies that are designed to be sufficient when the case is filled with a reasonable distribution of module types - ie some digital, some analog, some passive... although some are just because they are cheap...
I've never been a fan of the rackbrute - don't like the design - and the power solution is m'eh - rackwart & all - the only reason I would suggest a rackbrute was if someone was expanding a minibrute2/2s & even then it's at a push and based on space requirements & even then I'd be railing against them!!! even the branding is too much... if I had one and wanted to play out with it, I'd have to gaffe tape the back to hide the branding - lest 1/2 the audience thought I was playing an arturia synth - not just using one of their. cases for a modular!
in my experience the tiptop mantis is one of the better powered cases - no rack wart!!! - sufficient for almost all audio applications - not quite up to it if tryiong to power a full compliment of gen2 LZX video synth modules - because the -12v is too low - but not far off! but that points towards getting creative with analog utilities etc (doepfer are great for this)
the b-company "clone" of the mantis - the go case - on the other hand - is underpowered imo - due to them making the case 40% bigger but failing to upgrade the power supply which is apparantly a direct clone of the mantis one - which is probablyu= fine if you fill it with their roland and moog clones - but start putting a load of high draw digital modules in it and you end up in the sasme boat as the OP
doepfer 6u racks are also very well powered - the 9u ones seem a bit underpowered to me... haven't looked at the rackspace to power supply ratio in their bigger ones though... but again I suspect the 6 u are fine and the 12 u are fine - but the 8u not so much!
if you follow the formula in my signature (it scales well from tiny to bigger than you can imagine) you are likely to not have problems with power in cases that have decent power supplies
if you are building your own case and adding power I recommend the befaco excalibus power supplies as very good - 1 per 6u works well and they are very quiet - no noticable ripple up into video rates (MHz, not just KHz for audio), no rackwart, equal -ve and +ve rails and available DIY - a simple if tedious build (due to the number of headers that need soldering) - & low form factor - all headers are on the edges, not upright
btw - there's a great primer on modular power in the stickies of the 3u & 1u subforum at modwiggler... including why you need to leave a load of headroom - see previous post for synopsis
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities