Murata Power Solutions offers a compact adjustable output SIP power solution in its Okami series, which DigiKey offers as OKR-T/3-W12-C. The device has long exposed pins that seem ideal for a board-to-board mating solution. Which connector can you use to mate to this device?
The output header pins on this device are a proprietary Murata model with a nonstandard 1.7mm pitch, which keeps its overall size to a minimum for direct soldering to the PCB. The product is not intended for connectorized mating applications, but if you are determined and willing to sacrifice a few parts to testing and assembly, you might be able to kludge Mill-Max part number 871-43-021-20-001000 into working. This is the closest option DigiKey currently has in stock to the 1.7mm pitch used by Murata; I would not recommend this solution for anything beyond prototyping or product testing, but it may help get your project off the ground…