I have added a new Visual web part in an already deployed solution.
The new webart is not appearing in SharePoint Designer under
All files folder.
How to up[ate the existing solution with the newly added visual webpart?
Make sure the visual webpart is in the package in your visual studio project.
Update the solution with this command
Update-SPSolution -Identity contoso_solution.wsp -LiteralPath c:\contoso_solution_v2.wsp -GACDeployment
If the webpart is still not there, reactivate the feature or reinstall the feature.