Xbox One S turning on and off by itself

I have seen this issue before with an Xbox One S.. It would shut off for no reason. There wasn't a problem with the Internal Power Supply, Hard Drive or Overheating. It came down to a Motherboard Malfunction either with the APU, Power Management IC or
Motifs. Sometimes this issue can be caused by a bad A/C cable... it does happen but its a small percentage. It definitely was the MB that was the issue. I replaced the board for the customer and fixed the issue. Unfortunately I did not have any donor boards
at the time to replace the faulty components on the original board. Motherboards are pretty scarce and can be expensive.... especially now. I would give Xbox Support a call and see if they can help you out ( no sure if the repairs are in operation). Hopefully
they can give you a break on the repair.

It might be that a cord is unpluging itself and is turning off the xbox.

Hah, and there-in lies another issue with today's climate -- there's no stores open right now to take repairs and everything is backed up. So bringing it to a repair shop, Best Buy, or otherwise (they just closed the local Microsoft store 5 miles away
- now the nearest is two states and 200 miles away), so a professional repair is a time consuming ordeal too.

How old is your Xbox One S? It could be from overuse or just being old. I have a OG Xbox One and my power brick needed to be replaced. Im pretty sure the Xbox One S's dont have a outside power brick like the OG Xbox Ones do. Honestly as you said if this
is the issue just save your cash for the new Xbox One.

It could be your power outlet of you tried plunging in your Xbox at a difrent outlet? If not i would get new cords!!!!!