Give you a switch on how to look at it is isolated and non-isolated?
Isolated for high-pressure exchange, a transformer, the transformer is mostly core, but also useful magnetic ring
Non-isolated generally low-voltage direct current, no transformer, there is an inductor, high-power multi-purpose magnetic ring, low-power inductance with more
General low-voltage direct current is mostly non-isolated, high-voltage communication for the isolation
With a multimeter input and output side of the resistance, if very small or direct conduction is non-isolated, if the resistance is large, is isolated
