When we have cruised to smaller/older marinas we have found plug-ins for (modern standard) 30 twist lock, 20 amp, and 15 amp. Sometimes with rust on the boxes and some concern over whether our zinc's were at risk!
So we carry adapters for all, and just limit our shore power needs if using the lower amperage sources. Other than occasionally wanting to power up the coils in the water heater, we do not need too much "pass through" power for our boat's 12 volt needs these days. (Modern low-amp draw refrigeration and all-LED lighting has greatly reduced this outside power need.)