During a discovery it creates and updates CMDB records when it detects a running instance at the PostgreSQL level.

Per our docs it collects the name PostgreSQL instance@hostname. However, as by default we see in the related tree of several CIs with 'PostgreSQL' with in the cmdb_ci_db_postgresql_instance table.

Out of box we see this:

Step 19. Set label

Value: $instance 
Name: $name

This is the Output example:
'PostgreSQL'

In the related tree of the CI we see there are several PostgreSQL, listed in the cmdb_ci_db_postgresql_instance.

Do the following if you prefer to have the PostgreSQL pattern to populate the PostgreSQL@instance name.

Step 19. Set label
added the following:
Value: $instance + "@" + $computer_system.primaryHostname
Name: $name

This is the Output example:
'PostgreSQL@mikecamba'