[PostgreSQL] Post install error "Password authentication failed for user" when connecting to DB

So you decided that MySQL isn't to your liking and since the other alternatives aren't free enough, you tried out PostgreSQL. Freshly after your installation, you happily try to connect to your DB either via command line (\q guys.. \q seriously?) or pgAdmin, but are baffled when this message appears on screen:

FATAL:  Password authentication failed for user "Administrator"

because you did not remember creating a user during installation, and the only password you were asked to define isn't working.

The solution? Try to connect as postgres user:

psql -U postgres

If it's still not working, check under postgresql.conf if the listen_addresses parameter is specifying a correct and reachable address.