@Edent "Based on the three that I tried, PD chargers will not negotiate down to 1W levels."

It's not the chargers. The watch is simply missing the two 5.1k resistors connecting the CC1 and CC2 pins of the USB-C connector to ground that are required to indicate to whatever is plugged in that it wants 5v power.

USB-A to USB-C cables work because they provide 5v unconditionally. Anything that needs to care about which end provides the power (eg. a USB-C cable to a laptop) won't work.