Amazon.com: DC 5V Power Converter, DROK 5pcs Mini Voltage Buck Regulator DC 4.5-20V 12V 9V Step Down to 5V Reducer Transformer Board 3A 10W Adjustable Fixed Volt Output Step-Down Power Supply Stabilizer
DC-to-DC Converters: Design, Working & Applications
Amazon.com: Converter Module, DC-DC Buck Step Down Converter Adjustable Power Source Module 6.5V-60V to 1.25-30V 10A for Lithium or Lead-Acid Battery : Industrial & Scientific
power supply - Design considerations when combining multiple DC DC converter with the same input, but different output - Electrical Engineering Stack Exchange