PC Randomly Force Restarting

[YxriDev]

Hello, at the time of posting this I will most likely have my new custom PC built but I'd still like some answers regardless, just today, since plugging in a portable router (the one linked below) to test if it worked or not, my PC has been randomly and without reason force restarting, I had plugged in this device to make sure it actually worked as it was purchased today, and when I plugged it in without the battery to see if that worked, my PC screens went black, my motherboard reposted (with the single beep sound) and I was suddenly at the windows login screen again with everything closed, since plugging this device in, every 30 minutes to an hour it would complete the cycle again, black screens, motherboard single beep and windows login, I just now was closely monitoring the CPU temps to make sure it wasn't that, and they stayed around 65 degrees Celsius (every time this happened I was in the middle of a game which thankfully saves its own progress when I exit) I have yet to see if this happens without gaming as to be honest I don't have the patience and want to complete this game, but this sort of issue is completely beyond me and makes no sense, this has only ever happened once before, and I fixed it by cleaning my PSU but, even before cleaning it, the restarts we're never this frequent and never had some potential reason like the one stated above, when it happened it just did it. I hope you could please help me as I'd like to keep this pc to maybe use it as an RDP or a 2nd gaming rig for if friends come over, thanks a lot for reading. For anyone wondering, the only background processes I had open at the latest occurrence was the following: Brave (The application was open playing music), Roblox (The game I was playing), Multiscreen Blank, ShareX, Core Temp, Rainmeter, EarTrumpet and Off Remote Helper (I've never had any problems with this application before)

 

Router: https://www.amazon.co.uk/dp/B081S5KRZ7/