Hi Damir,
Thanks for contacting Syncfusion support.
We request you to provide the following details for clear understanding of your requirement
1.Let us know if you trying to fill other input controls with data based on the value selected from the dropdownlist in cascade. If yes, then what are the values you need to update input elements and how many input elements are placed in that form.
2.Regarding query "onSelect event without calling postback to controller “do you need client side onSelect event?
3.What would you like to process on select event in Dropdownlist?
With the provided information we would be able to understand your requirement better and provide an appropriate solution.
Regards,
Prince