A transformer without coil racks includes a winding set, multiple conductive plates and an insulation mounting sheet. The winding set includes a coil portion and a magnetic core set running through the coil portion. The magnetic core set includes at least one inner magnetic core portion and at least two outer magnetic core portions that are spaced from each other by a gap. Each conductive plate includes a connecting section and two extended arms connected to two ends of the connecting section and running through the gap. The insulation mounting sheet includes multiple retaining slots corresponding to the gap to allow the extended arms to pass through and multiple retaining portions each being formed between two neighboring retaining slots to prevent the extended arms from contacting each other. The conductive plates run through the retaining slots and are confined by the retaining portions from moving.