If your vCenter server has a self-signed certificate, you will get a warning about this when connecting to it from vSphere PowerCLI. You can disable this warning through PowerCLI with the Set-PowerCLIConfiguration cmdlet.

1. Start an elevated vSphere PowerCLI (right-click, Run as Administrator).
2. Enter the following cmdlet:

   Set-PowerCLIConfiguration -InvalidCertificateAction Ignore

   Press Enter again to confirm the change.

After making the change, new connections to the vCenter server will no longer produce a warning about the certificate.