Similar in purpose, extremely different in implementation, since PoE-supporting Ethernets (e.g. 100base-TX) are magnetically coupled, but PoDL-supporting Ethernets (e.g. 100base-T1) are capacitively coupled.
The windings in isolation transformers are inductively coupled through the magnetic field in the core. There's often a shield between the two windings to reduce any capacitive coupling.
The industry standard for SPE is moving towards a transformer as well, because to get 1,5kV in isolation from a capacitor requires large components. A transformer is a lot smaller and provides common mode rejection.
