A magnetic assembly is disclosed. The magnetic assembly includes a first magnetic core, a second magnetic core and a first series winding. The first magnetic core has a first top surface, a first bottom surface, a first sidewall, a second sidewall, at least one first sidewall through-hole and at least one second sidewall through-hole. The second magnetic core is connected to the first top surface of the first magnetic core. The first series winding has a first upper winding set, a first sidewall winding set, and a second sidewall winding set disposed on the first top surface, the first sidewall and the second sidewall respectively. The upper winding set is connected to the lower winding set via the first sidewall winding set and the second sidewall winding set is further connected to the lower winding set, so as to form the first series winding around the first magnetic core.