How can I disable popup notifications?

Solution 1:

From official info:

Hiding notifications

If you are working on something and do not want to be bothered, you can switch off notifications.

1. Open the Activities overview and start typing Settings.
2. Click on Settings.
3. Click on Notifications in the sidebar to open the panel.
4. 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.

Solution 2:

The loose power connection will kill your battery, when it is connecting/disconnecting 5 to 20 times per minute. You'd better fix it, before worrying about the notification.