How to fix the issue: "The specified database user/password combination is rejected" using-CodePudding

I'm using Spring application and stack is like: Java 11, Spring Boot 2.2.1.RELEASE.

(technology versions may vary here)

When I try to connect to the database via Data Source using Intellij IDEA, I get always the issue like:

The specified database user/password combination is rejected:
[28P01] FATAL: password authentication failded for user 'postgres'

How can I fix it?

To be noticed: this answer is similar, but not related to:

To clarify: provided example is for PostgreSQL, but it can be another database system.