Abstract: This invention discloses an improved ring-core transformer which includes a ring core, a pair of coil former, a frame body, a pair of protrusions, at least one row of pin bases, a plurality of connecting pins and coils, wherein the coils are respectively wound on the pair of coil former. Each coil has a plurality of output terminals leading therefrom and is connected to the pins by being passed through the gaps between the pin bases and fixed in the slots formed on the pin bases. Therefore, the ring core transformer of this invention can offer excellent insulation by the isolation of the terminals also provide a wide range of output voltage.