Abstract: The present invention provides an improved transformer (20), which broadly includes: a substrate (21) having first and second surfaces (22, 23); a first board (24) mounted on the substrate first surface; a second board (25) mounted on the substrate second surface; the boards being identical to one another and being mounted on the respective proximate substrate surfaces as mirror images of one another; each of the boards having a plurality of dielectric layers with electrically-conductive sheet windings (35, 36, 37, 38) embedded therein; and an assembled core (26, 28) operatively arranged to provide a path for magnetic flux attributable to a current in some of the windings. Third and fourth boards (71, 72) may be piggy-backed onto the first and second boards, respectively, to selectively vary the properties of the transformer.