DC-to-DC power supplies for CPUs or GPUs are critical components on the motherboard of modern computer systems. Converting an intermediate bus voltage (e.g. 12 V) to the core voltage (∼0.9 V) of CPUs or GPUs must be efficient, compact and cost effective. This paper proposes an active-clamp forward converter (ACFC) power block to supply core voltage on a motherboard. The ACFC power block can be individually tested prior to assembly and vertically soldered onto the motherboard to save motherboard area. A low loss, compact planar transformer is designed into the ACFC power block PCB. A custom, standing slab inductor not only provides high inductance and high saturation current but also helps to mechanically support the power block. A one-piece copper winding connects the transformer to the inductor, thereby reducing the DC loss in the current path. Experimental results show a peak efficiency of 90.4% with a 12 V input and 0.9 V output for an output current of 25 A.