Abstract: The transformer has a pair of cores, a winding assembly, a primary coil and a secondary coil. Each core has a center and an elliptical central core formed at the center. The winding assembly has a body and two mounting brackets. The body is a hollow elliptical column with two ends and has an outer surface and an elliptical mounting hole. The two mounting brackets are attached respectively to the two ends of the body, and each mounting bracket has a slot with a rounded edge and multiple pins. Since the central cores are elliptic, each central core may have a larger volume, such that the transformer may have a greater heat-absorbing capability, so transformer temperature rises slower. Furthermore, the winding assembly mounted on the central core is more stable, and even if the pins detach, the winding assembly will remain in position.