During my first run of trying to upgrade the external PSC, I entered the PSC Appliance FQDN, HTTPS port, SSO user name, SSO password and the appliance root password. I filled in the information for the ESXi host that is managing the appliance and hit next.

After an SSL warning (to be expected) prompt, I saw the following screen with the heading “Upgrade - Stage 1: Deploy vCenter Server”

The upgrade wizard has detected my appliance as a vCenter server and not a PSC. That’s not right. So I went back and specified the source PSC’s IP address, hit next and was presented with the following screen with the heading “Upgrade – Stage 1: Deploy Platform Services Controller

And now it seems to work:

I’m not sure if it’s something in my environment or a bug in the install wizard, but this certainly had me confused for a short while.