Transformer, Power Module and Switching Power Supply

The disclosure provides a transformer, a power module and a switching power supply. The transformer comprises a magnetic core, a primary side winding and a secondary side winding; the magnetic core comprises a first cover plate, a second cover plate, a winding column and at least two side columns, and at least two side columns of the magnetic core; at least one of the side columns has a through channel, the primary side winding is wound around the winding column, and a lead wire of the primary side winding passes through the through channel; the lead wire of the secondary side winding passes through a gap formed by the at least two side columns. In the disclosure, the lead wire of the primary side winding can pass through the through channel, thereby saving space and improving power density of the switching power supply.