Hi Doug,

The PrincipalSearcher FindAll method returns a collection from the StackOverflow How can I get a list of users from active directory thread, which you can use to feed the DataSource, DataTextField and DataValueField properties of the ComboBox.  You can also check these articles: 

https://docs.microsoft.com/en-us/dotnet/api/system.directoryservices.accountmanagement.principalsearchresult-1?view=netframework-4.8

https://docs.telerik.com/devtools/aspnet-ajax/controls/combobox/data-binding/binding-to-array-or-arraylist.

If you implement a runnable sample, you can post it in the Code Library section and you will get rewarded with 3000-5000 Telerik points.

Regards,
Rumen
Progress Telerik