An isolated switch-mode power supply includes at least one input, at least one output, and a power circuit coupled between the at least one input and the at least one output for converting an input voltage or current to an output voltage or current. The power circuit includes a transformer having one or more primary windings, one or more secondary windings, an electrical insulator, and a core magnetically coupling the one or more primary windings and the one or more secondary windings. Upper portions of the primary and secondary windings are covered with the electrical insulator. Other example switchmode power supplies, transformers, magnetic chokes and methods are also disclosed.