For an Android phone with a broken power button, it seemingly impossible to restart the device using a conventional way.
Fortunately, you should be able to restart it by the help of a USB cable and computer/laptop.
Because in this tutorial, I will show you how to restart an Android phone without the power button that should work on any brands, any version, both rooted or un-rooted.
Note: This method is only for an active Android phone (turned on). An inactive (turned off) phone won’t be able to use this method since the necessary service is not running.
1. Go to Android Settings > About phone > Tap Build number multiple times until you see a message that you are a developer now.
2. Next, head to Android Settings > Developer options > USB debugging.
3. Connect your Android phone with a PC or laptop via a USB cable. After that, you would see a notification that USB debugging is connected.
5. Extract, and run adb-setup.
6. Type y on all questions, then press Enter.
7. You may see a warning like this. Just click Install to confirm.
8. Locate this directory C:\adb
9. Click File > Open Windows PowerShell.
10. Type adb devices and press Enter. It will show you the serial number (IMEI) of the connected phone.
11. Type adb reboot and press Enter. It will soon restart the phone.
12. Wait until the phone restarted, then you can unplug the USB connection and close Windows PowerShell.
ADB was a part of a bigger program called Android Studio. Now you can use it to restart your phone while the power button is not working. However, this method is just a temporary solution — get your phone fixed for a better experience.