Don't we have technologies for that like fuses?

In particular, people seem to use untrusted AC power outlets all the time without their devices being fried. The motivations of an attacker who wants to fry devices (mere lulz) and the motivation of an attacker who wants to break into working devices silently are very different; it makes sense to expect more of the latter, and to define the latter and not the former as within your threat model.