PD has a variety of power profiles, different current and voltage. Neither the consumer nor provider need to support all power profiles. Supporting one power profile doesn’t require a device to also support “everything below that level” or anything like that. It’s possible that one of those devices in the chain is doing conversion.

I have a 100W laptop power adapter for my InfinityBook that can’t charge one of these power stations, for example. A different 100W adapter works fine, IIRC at a reduced rate.

This usecase should work fine. Seeing that it also works with the anker powerbank, maybe your ugreen powerbank is the issue and doesn’t have a proper implementation