I think Lugia alluded to this, but I'll go into a tiny bit more detail:
When you first power on your case, there's a spike in current. Everything is snapping on all at once. Your modules might draw a certain amount of power once they are on and warming up. But the instance that you turn on the case... spike.
This is especially the case if you're using tube gear for example. Manufacturers like Erica created a line of tube modules and part of the work around was a secondary power supply to handle the additional overhead in power when turning the module(s) on.
Are you relying on Modular Grid to tabulate your amps or have you worked this out for yourself? Some modules on here have the wrong power values and some don't have any at all. So don't take what you see on MG as gospel. Do the math yourself and see how close you're pushing to the maximum. You can get the specs directly from the manufacturers.
A fuse is your last line of defense from some really nasty outcomes (including a FIRE). It's worth the time to investigate. Depending on your set-up... you just might need a larger power supply... or have a bad module or bad power supply.