Power supply system (100) comprises vertically sequentially a QFN leadframe (101), a first chip (110) with FET terminals on opposite sides, a flat interposer (120), and a second chip (130) with FET terminals and the terminals of the integrated driver-and-control circuit on a single side. Leadframe pad (107) has a portion (107a) recessed as pocket with a depth and an outline suitable for attaching the first chip with one terminal in the pocket and the opposite terminal co-planar with the un-recessed pad surface. The interposer comprises metal patterned in traces separated by gaps; the traces include metal of a first height and metal of a second height smaller than the first height, and insulating material filling the gaps and the height differences; one interposer side attached to the leadframe pad with the first chip, the opposite interposer side attached to the terminals of the second chip.