Xbox one s turn off after a couple seconds after hitting power button

I will suggest checking your device physically with someone who has any hardware expertise or if your device is under warranty then check for servicing. Please click the below link and follow the steps:

Getting your Xbox device serviced
https://support.xbox.com/help/hardware-network/warranty-service/getting-your-product-serviced

• Hi, and thanks for reaching out. My name is Shubham. I hope you are well. I'm an Xbox Independent Advisor. I am happy to help you today.

Please check the Power Supply, Make sure that the power supply is securely connected to both the Xbox One S and the power outlet. If the power supply is loose or damaged, it can cause intermittent power issues.

I have swapped out the power supply with a new one. The old one wouldn't do anything. The new one has this symptoms. I've tried unplugging the HD and DVD drive with no change.

Turns itself off a couple seconds after pressing the power button even while holding the sync and eject

Hi, power the xbox and controller on, then press and hold the power button on the xbox for 10 seconds.

When the xbox powers off pull the power cord out of the back of the xbox and wait two minutes. Reconnect the power cord and press the power button on the xbox to power it on. Power on the controller and then try using the controller to power on/off the xbox.

This solution worked. Thank you!

For anyone else reading having this issue, I still had to re-sync the controller after going through the above process, in order to solve that problem. After turning on the Xbox one with the power button sync it the normal way by hitting the sync button
on the front of the Xbox One S, and then holding the sync button on top of the controller. Thereafter, the guide button on the controller will power on the console.

However, the above solution did immediately fix the fact that the controller wouldn't turn off when I powered the console off.