The ASPxCombobox allows its items to be loaded from the server on demand, via callbacks, if its EnableCallbackMode property is set to true.
For instance, list items that are not currently displayed within the editor's dropdown window, can be dynamically loaded, when an end-user
scrolls the list. In this mode, the CallBackPageSize property defines the number of items to be obtained from the server each time
it's required. This mode makes the first page load much faster, since only a few items need to be loaded initially.