The Add-WindowsPSModulePath command adds the default Windows PowerShell module paths and the content of the machine level PSModulePath variable, to the end of the $env:PSModulePath variable.

For example, before the command is run, $env:PSModulePath may be set to the following:

C:UserswhoamiDocumentsPowerShellModules
C:Program FilesPowerShellModules
c:program filespowershell6-previewModules
C:WINDOWSsystem32WindowsPowerShellv1.0Modules

After the command has run, $env:PSModulePath will have the following added. These values are hardcoded:

${env:userprofile}DocumentsWindowsPowerShellModule
${env:programfiles}WindowsPowerShellModules

In addition to these, any paths present in the environment variable are added. This process may result in some duplication. The outcome is shown in this screenshot: