Thanks for the help guys.
I opened up KerbalismSimplex\Support\SimplexNFEIElectric.cfg and removed this section. Will probably probe a bit more to find the exact line causing issues, but for now I'm happy just removing the whole block.
This brought back power generation and the nuclear control panel.
I'm sure there'll be some more weird edge cases, but this is now the closest to a 'perfect' modset for me. RemoteTech, KerbalismSimplex, and Outer Planets to add logistical challenges, and Near Future to help tackle them.
Cheers!