I don't! - at all
It's isolated in exactly the same way as a conventional mains transformer, with a transformer providing isolation between primary and secondary. The components connecting across the isolation barrier (where fitted) are there for safety reasons, and are also present in units with conventional transformers for exactly the same reasons.
It all depends if the appliance is a Class I or Class II device, SMPS or conventional transformer makes no difference.
You can have SMPS's which aren't isolated, but you can also have conventional ones that aren't either.