psql won't list databases
According to the pg_hba.conf snippet, a password is required if you connect from ::1, which is the IPv6 address for localhost.

It may be that the box on which you have the problem has the resolver configured so that the name "localhost" refers to both 127.0.0.1 (IPv4) and ::1 (IPv6), so that the command psql -h localhost... may connect to one or the other address. 

I'd suggest to check the /etc/hosts file for different localhost entries, or bypass the resolver by connecting to 127.0.0.1, or update the pg_hba.conf with "trust" for IPv6 local connections.