Capacitive Galvanic Isolation
There is no DC path between the in and out. Yet why doesn't this work or is used?


With galvanic isolation you usually want protection from AC mains and not just from DC. But AC voltage passes right through your capacitors - the voltage would still be lethal!

You can see these caps e.g. in audio amplifier outputs. You only want the AC component on your speaker or headphone coils.