Sounds like you changed it to a different refresh rate at one point and forgot about it.

I wouldn't worry about it, probably just some gremlins. 

If Win 10 updated your OS files or Nvidia drivers -- that is probably why you saw a change "On Reboot"
 
Some updates changes that are "loaded" do Not take effect until after the PC restarts

Like i said i have the newest nvidia drivers.

It happened not immidiately ( not on pc first power on ) power outage.
But on second time ( second turn ) when i boot to Windows 10. On my second turning on pc, second boot to windows. So not immediately after power outage. It happened very short time after power outage ( my second turn on computer ).

To make again 144hz i turned off monitor and turn back on again.


So that was power outage related or not?

Maybe, as power interruption does not allow Windows to do its proper save & shutdown routine ...
 
Could be Win 10 on restart did not properly identify the monitor, so it changed the refresh.
 
If it happens again, before changing anything or power off/ on monitor, look in Device Manager and see how your Monitor is listed
 
Maybe one of the other Forum members has a different idea or knows which log file to look at
 
If it has not happened again, I would not be concerned

The first thing you need to do is to move the PC power plug onto a circuit not on the same line as the kitchen

tmmy34, Fuse or breaker. A fuse is an antiquated single use disposable device to provide overcurrent protection.
Fuse > Breaker >
But anyway. Was this the main breaker of the power panel?
The main breaker is the biggest breaker and should be a two-pole (in some cases four-pole) that feeds the two buses for all of the other breakers in the panel than feed the branch circuits of the house.
 
 

I understand what you are writing but...
What is "turn on kitchen"? What do you mean by the kitchen was or got turned on? Powering on kitchen = ________
 
Could be that just before the "all power in house just went out" their was a voltage spike and could have altered your monitor to a lower (factory stock setting?) refresh rate.
 

So your family keeps the power to the whole kitchen off until needed?
Is the kitchen being worked on or renovated? This would make sense so no one gets electrocuted.
Or a standard practice.. a daily event... normal operations?
 
But back to the issue, are you getting this refresh rate indication from Windows or seeing it in the monitor's settings?
 
Edit: Just curious but where are are you? What is your geographical location?
 

Well from a technical standpoint, I would think the monitor has suffered a voltage spike or even under voltage and maybe damaged. If the monitor keeps reverting to a lower refresh rate when turning it on after a period of time of being off or after the power goes out repeatedly it could be only the beginning of problems especially the keeps dropping out inexplicably.
 
Electrical equipment are sensitive to current changes high and low and should be plugged into a steady/stable supply of power. One low cast line of defense would be a surge protector but only useful for when voltage spikes higher than the rating of protector. Pricier options would be an Uninterruptible Power Supply or UPS in short.
 
Bottom line is a computer and it's peripherals should be plugged into a known reliable and stable power source. 
 
Edit: In the mean time, talk to your family and ask them to inform you when they might go to turn on the electric oven in kitchen so that you can turn off your computer and if the power does go out it could minimize any impact to it.

i think your fine. i would definitely purchase a quality ups for your system. if this happens again theres a good chance your hardware could be damaged. i would get something like this
https://www.newegg.com/Product/Product.aspx?Item=N82E16842102131
you may not need that high a wattage ups but make sure its a quality brand like APC, tripplite or cyberpower.

Ok so listen. This not happened again. I turn off pc for overnight ( after a period of time of being off ),and turn on in morning and all fine. Windows 10 boot with 144hz. So this happened once after power outage. What you think. It was related to outage or coincidence ?

Really sorry for my language. If i can i explain this more clearly.

Pc was running in fire strike benchmark with monitor ON.
At the same time my mother was powering on electric oven in kitchen.
And then power went out in house.

Just before power went out, pc was running in Fire Strike test, and monitor was on. 
When power went out,pc goes off and monitor goes off.

When power back ,monitor turns on itself . Then I booted pc , all was looking fine, Windows 10 booted with 144hz

But after moment I shutdown pc by clicking shutdown in Windows 10 and I manually turned off monitor.
After 30 minutes ,first I turn on manually monitor,then I boot pc again. Windows 10 booted with lower refresh than 144hz.( on nvidia panel still 144hz )
 

To restore 144hz I just turned off monitor and turn on again. And this not happened since.
 
And I am not able to reproduce. Turning off pc few times and booting again,and nothing,still 144hz. Even I cut power 3 times to check,but still 144hz on boot.

So maybe that was glitch.windows,system,drivers or something but not related to that power outage? Or maybe power outage was the reason, but the problem didn´t show up immediately?

yes fuse blew and shut down all the power to the house correct

I am living in Poland. I try explain more clear issue.

My pc was running in 3dmark. Then in moment when my mother turn on oven in kitchen power goes out. Reason was bulb inside oven. All house without power. Then she goes to fuse box and something change i dont know what exactly. But power back to electrical outlets in house. Only lights was still off. Lightning at home was off and not able to turn on back. So if power to electrical outlets back i try to run pc. Windows 10 booted first time with 144hz without issue. But after moment i shutdown pc by clicking shutdown in Windows. And after moment i booted pc again ( second time ) and in this moment Windows 10 booted with lower refresh than 144hz,that was propably 120hz or 60hz . To revert 144hz i just turn off monitor and turn back again. Thats all.

House was still without lightning. Only electrical outlets was powered.

And my question is.

That refresh thing was related to fuse,monitor firmware or just system? House on this moment was without lightning only electrical outlets was with power.


Later after changed fuse ( when lighting in home back ) when i tried to reproduce issue , i cutted few times power and i cant reproduce. Pc booting ,shutdown,restarting with 144hz still.