Abstract: An AC adapter for use with a portable computer has a primary transformer disposed within a plastic housing. A shielded heat sink assembly is positioned in the housing between the transformer and a facing interior side surface portion of the housing. The shielded heat sink assembly includes a resilient block of thermally conductive, high dielectric strength silicon material pressed into contact with a thermally conductive copper heat transfer band wrapped around the housing of the transformer. From its contact area with the copper band the silicon block extends through an opening in a black-colored plastic radiant shield sheet and is adhered to the inner side of a copper heat sink sheet with a thermally conductive adhesive material that also adheres the outer side of the plastic shield sheet to the inner side of the copper heat sink sheet. The outer side of the copper heat sink sheet is adhered to the facing interior side surface portion of the housing with thermally conductive adhesive material.