Here is a complete listing of the main component.
import QtQuick 2.0
import QtQuick.Layouts 1.3
import QtQuick.Controls 2.4
 
 
Control {
    padding: 20
    contentItem: ColumnLayout {
        spacing: 10
 
        RowLayout {
            Layout.alignment: 
Qt.AlignLeft
 
            Label {
                text: qsTr("Device type:")
            }
 
            ComboBox {
                textRole: "name"
 
                model: ListModel {
                    ListElement { name: "DummyClient"; source: "DummyClientComposite.qml"}
                }
 
                onActivated: loader.source = model.get(currentIndex).source
            }
        }
 
        Loader {
            id: loader
 
            source: "DummyClientComposite.qml"
        }
    }
 
    property alias source: loader.source
}