How to add a New Target Application to an existing Secure Store Service Application with PowerShell?

I have an existing Secure Store Service Application with one Target Application in it. I'd like to add another target application using PowerShell. Scripts I have found so far always want to make a new Service Application with the Target Application named the same.

I thought to modify the the script, skipping the step of New-SPSecureStoreApplication, but the Get-SPSecureStoreApplication demands a -ServiceContext URL. Why is this connected to a URL? Is it the URL for Central Admin?

And I don't see how to tie the new target application to the existing Secure Store Service Application.

Please advise.  Thanks.