I have just install Postgres 9.3 on Windows 7. The installation completed successfully. It has never asked me to provide the password for postgres user.
Through trial and error I found that the password for Postgre SQL 10 for the username postgres is "admin". I kept typing in different password until I reached that password. I am using pgAdmin 4 to test out my SQL Statements, POSTGRE SQL 10 is the first server connection set up using localhost.