Planter: Auto-generate Plant UML diagrams from Postgres tables
github.com
github.com
My impression is that the maintainers are Oracle-centric (I don't interact with the project with any regularity, so this could be mistaken), but I use this with PostgreSQL and have been quite pleased.
Imports from MySQL, PostgreSQL, SQL Server, works with Rails, Django etc.
The Plant UML CLI itself has some limitations if the ER diagram is really large.