The passive devices in state-of-the-art miniaturized DC-DC converters are generally integrated on-chip and in-package. Nevertheless, the quality is poor-to-moderate, thereby compromising the power-efficiency. In this paper, we propose the miniaturization of the DC-DC converter by means of realizing its passive devices as embedded devices that are printed within a high-density 3D inkjet printed-circuit-board (PCB). We propose a fourth-order stacked LC filter embodying passive components with small values—effectively at no additional cost because they are embedded through 3D-printing. For the inductor and capacitor, we propose to adopt a high-Q solenoidal structure and the metal-insulator-metal planar structure, respectively. The proposed filter is printed within the 3D-PCB with a compact 124 mm3 volume due to the stacked arrangement. The measured AC attenuation is 21.2 dB at 200 MHz. The filter is further verified by means of computer simulations of a DC-DC buck converter. Simulation results of the converter employing the filter show a low output voltage ripple at 146 mV and a high peak power-efficiency of ~78% at 200 MHz switching frequency with 150 mA load current.