I have a product design which requires a power supply to be embedded into it, very similar to a smart plug. I don't want to go through the hassle of redesigning an entire power supply to fit within my scope. Do pre-certified designs exist that be incorporated into the same circuit board as the rest of my components? I understand I would need to go through FCC and UL certifications again, but I wanted to get a starting point for this rather than waste my time with a new design.
There are approved more-or-less self-contained board-mounted off-line SMPS modules, probably what you are thinking of. Sort of a SMPS wall-wart that can be PCB mounted.
There are approved PCB-mounted transformers. You can make a linear supply with such a part trivially, and use a DC-DC converter module or IC if necessary (or linear regulators).
There are, of course, DC-output wall-wart and brick power supplies that are approved, as well as AC-output wall-warts.
Many power supply chip manufacturers have "reference designs" that are available to integrate into a larger schematic. These come with BOM's, recommended board layouts, and sometimes a chip is so popular that a magnetics company will design and produce a transformer for it, eliminating a significant design cycle and NRE cost. Power Integrations is famous for this.
The next step down are the circuits on just about every datasheet and app note. Often the circuits need tweaking to fit a particular application, and very few come with transformer designs attached.
You don't say anything about voltages, currents, topologies, power levels, application, or application environment, so the above is probably irrelevant.