From official info:
If you are working on something and do not want to be bothered, you
can switch off notifications.
- Open the Activities overview and start typing Settings.
- Click on Settings.
- Click on Notifications in the sidebar to open the panel.
- Switch Notification Popups to off.
When switched off, most notifications will not pop up at the top of
the screen. Notifications will still be available in the notification
list when you display it (by clicking on the clock, or by pressing
Super+V), and they will start popping up again when you switch the
switch back to on.
You can also disable or re-enable notifications for individual
applications from the Notifications panel.
in your case, you are probably ok with disabling Power notifications
PS: To open Activities overview press the Windows key. You can also get to Settings via the down-arrow at the top right.