This is not a built-in functionality of the dropdown list contained in the Power Table component. The configureEditor Extension Function gives the option of configuring a custom editor using an instance of javax.swing.table.TableCellEditor. You might be able to achieve this functionality using a custom editor. This requires some knowledge of the Java Swing API.
You will need to create an instance of the javax.swing.table.TableCellEditor class, write the code for the dropdown functionality, and return this with the ‘editor’ attribute from the configureEditor function.
See the following forum post for an example of creating an instance of the javax.swing.table.TableCellEditor class: Power Table with three dropdowns