A magnetic assembly includes a magnetic core and at least one foil winding assembly. The magnetic core includes plural magnetic legs. At least one magnetic path is defined by the plural magnetic legs collaboratively. Moreover, at least one low-permeability structure is formed in at least one specified magnetic leg of the plural magnetic legs. The at least one foil winding assembly is wound around the specified magnetic leg. Consequently, plural winding parts in a multi-layered arrangement are sequentially stacked on the specified magnetic leg. A direction of a conductor thickness of each winding part is perpendicular to a direction of a magnetic flux through the specified magnetic leg. The plural winding parts are gradually close to the low-permeability structure along an arranging direction, and the conductor thicknesses of at least two of the plural winding parts are gradually decreased along the arranging direction.