I'm definitely not an expert on this subject but I have seen references to "medical grade" power supplies and with a little help from google I found this:
I believe the key points are the AC leakage and the physical layout of the board and parts, with an eye on failure modes.
Regarding local codes, I believe no two are the same. Here in the US the NEC as a basis with local codes modified by some rules that I've never understood.
Also I've never heard of an insurance company denying a claim because the homeowner did their own work. Now lawyers..... that is a different story. Here in the US we are clearly litigation crazy :(