How come systemctl status postgresql.service and systemctl status postgresql@10-main show different results?
Ubuntu and Debian

If you're using Ubuntu, rather than using systemd's systemctl to gauge the status of your clusters use the distro's own pg_lsclusters. It'll tell you if they're running and the port number,

$ pg_lsclusters 
Ver Cluster Port Status Owner    Data directory               Log file
9.5 main    5433 online postgres /var/lib/postgresql/9.5/main /var/log/postgresql/postgresql-9.5-main.log