Cisco's SF/SG 300/500 series managed switches have CLI access via Telnet and SSH but this is turned off by default, leaving only the web interface to manage the switch. You can enable Telnet and/or SSH via the web interface, enabling management via CLI.
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.
Set-PowerCLIConfiguration -InvalidCertificateAction Ignore
After making the change, new connections to the vCenter server will no longer produce a warning about the certificate.