I am assessing the feasibility of using the USB Power Delivery Specification for a portable medical device application. The intent is to provide convenient charging through USB-C, using the 9V/3A specification. In this use case, the AC-DC transformer will be of unknown origin and quality, and therefore we must provide mains isolation within the device itself. We have used 1:1 DC converters in the past for lower power applications, and have had luck with integrated devices intended for this application (up to 500mA).
I am having trouble finding an equivalent solution for the higher power USB-PD, 27W. Most of the isolated DC-DC converters that I've looked at require a step down in voltage or do not provide sufficient power output. I would be looking for an input voltage range of 4.5 - 9V. The output could be regulated down to 5V, or could be regulated after the isolation.
I would appreciate any advice on this or any recommendations of products that might meet my needs.