I’ve never had any Erica Synth case, so I have no direct experience with them. I did build a bunch of cases using Meanwell PSUs like the R-60B and RT-65B, and some things might apply here as well. From the top of my head the things to watch out are: since Erica uses a Meanwell brick it’s likely that modules like Make Noise Pressure Points and Rene won’t work correctly, since they need a PSU that connects to earth (it’s an easy fix in case, just swap the brick with one that does connect to earth).
The other downside is that you probably have quite a bit of noise and ripple. If you don’t use any dodgy modules, do not need to boost signals either inside the modular or getting out of it and do not need to do do lots of multitrack recording you are usually fine.
I did some tests some time ago using a small skiff and a RT-65B PSU (which is this one: https://www.meanwell-web.com/en-gb/ac-dc-triple-output-enclosed-power-supply-output-rt--65b, so not the same as what Erica uses, but might be similar, but probably worse).
The test was more or less like this (not super-accurate, nor scientifically thorough, but it might give you an idea).
I did patch Braids into the Colour Palette (which I would say is a pretty decent VCA) and the output from the VCA (so from one channel of the CP) to my Presonus Firebox audio interface. I set the volume of the audio to roughly 0Db in the DAW (Reaper). Then I disconnected Braids from the VCA and looked at the peakmeter. I got a noise floor of about -58Db (peaks). Then I plugged the output of the sum of all VCAs into the audio interface and I got -57Db of noise (probably because each VCA is picking up a bit of noise from the PSU). Last thing I did was to patch the output of the CP into a Doepfer 138a linear mixer (which isn’t really intended to be an audio mixer, and even less an end-of-chain mixer), and I got about -54Db of noise.
What does this mean: well basically that even with my really less-than-ideal switching PSU noise seems to be slightly below the audible level. Actually if you make some music with lots of stuff going on I think even -30Db would be hard to hear. Of course ymmw depending on the type of music you make (very quiet ambient is probably a different thing than super-loud dubstep). What could increase the noise floor is using preamp modules, distortion, waveshapers and anything that will apply a gain that goes above unity.
Another common problem situation is multi-track recording. Let’s say you record your modular in multiple takes. I did a test with the previous config, using the output of the Doepfer mixer (just to get a kind of bad-case scenario). I did record silence (just the output from the module without anything patched into it) and copy-pasted this recording onto 10 tracks, so that all of them would play at the same time.
The noise now was -36Db and pretty audible by itself. Now of course this is not a realistic example. When doing multi-track recording you would not record everything with peaks being at 0Db, you’d probably record them much lower. With each track attenuated by 12Db, I get a noise floor of -50Db. But of course if you start to add a bit of compression and eq It might go up a bit. Still, not ideal, but also not really super bad.
I hope this gives you a better idea of what to expect from the Erica Case, even if of course that’s a different circuitry, so it might behave very differently (though as I said, I think it’s probably better than my example here).