It is not possible to change the voltage via the application, nor is it possible to set a specific power output such as 200 W or 350 W. The device operates with a standard input voltage of 110-230 V AC and supports a maximum load of up to 2500 W, but these parameters are not user-configurable in the app. The app can be used to control the plug, measure energy consumption and program schedules, but not to change the voltage or set a custom power limit.
The Shelly Plus Plug S does not require an active WiFi connection to store and execute switching schedules "offline" in the device. As long as the schedules are stored in the device, they can be executed even without a WiFi connection. You can therefore use the plug to restart your router automatically by setting the switching times accordingly.
However, to configure the switching times, you must first establish a WiFi connection to access the device's web interface and make the settings.