Don't Set Users Up For Failure: Use Password Guides
Sites that have password restrictions such as minimum characters, required special characters and other restrictions but do not display a guide explaining these requirements are setting users up for failure.
Don't have users take a test they didn't study for only to see the answers after they fail. The NNGroup emphasizes this point in their recommendations for website form usability
Password Strength Meters Help
A password strength meter is not required, but it can be helpful. Its ability to show users the strength of their password reassures them that they are making their account secure. See Maslow's Hierarchy of Needs for the necessity for psychological safety.
If a password strength meter is shown, you should explicitly mark the minimum strength allowed for an acceptable password. Without this, the feedback mechanism fails.