My Series S turned its self on last night.

"neither my One X or Series X have installed system updates when turned off...they wait until I turn the thing on"

If power mode is set to Instant on, the console will check for System updates automatically.

If power mode is set to Energy save it wont check for an update until after it's turned on and connected to the Internet.

After you power up the console, if an update has gone passed the Mandatory time the console will launch the update and install it.

If the update has not reached the Mandatory time it will operate as normal until that time is reached and then launch the update.

For example, you may turn your console on for a all night early morning gaming session with your friends and there was a system update released earlier that day. If your gaming session goes past the Mandatory time for that update while you are playing a game etc, usually 3 am in the US 8 pm in Australia, the console will initiate the System update.

It's always better to check for an update using Guide>Settings>System>Updates before getting into a all night gaming session.

If you leave your smart TV in standby and still connected to the net, I would expect automatic updates.

is it supposed to turn on though?

As stated above this occurs when the console checks for a system update and the time, 3am, is around the time when its mandatory to update, US time.

During the stage between Verifying and Applying, when the consoles restarts during the update, the Xbox button on the console will flash or pulse about 15-20 times for a XBox OneX and about 6-10 times for a Xbox Series X.

So, the consoles are designed specifically to turn themselves on in the middle of the night to run updates? That is a seriously bad design if you ask me...there's no reason for it to do that. None of my other electronics turn themselves on...my TV and PC both update when I turn them on. Looks like I'll start unplugging my Xbox at night in that case.

Having said that, neither my One X or Series X have installed system updates when turned off...they wait until I turn the thing on

is it supposed to turn on though?

As stated above this occurs when the console checks for a system update and the time, 3am, is around the time when its mandatory to update, US time.

During the stage between Verifying and Applying, when the consoles restarts during the update, the Xbox button on the console will flash or pulse about 15-20 times for a XBox OneX and about 6-10 times for a Xbox Series X.

I have this problem all the time with my Xbox one I got used to it. It hasn’t really caused any problems for me I think it might be doing some kind of self maintenance or something.

is it supposed to turn on though?