Weirdest lag and weirdest "solution"?!

Hey everyone,

Couple of days ago I bought new XPS 13 2 in 1. Everything was fine, until I noticed one very strange thing.
I bought my favourite game and only game I play, Football Manager 2020.

So, the problem is, when I run game on battery everything is fine but when I run it on charger matches become laggy. I was searching for solutions and I believe I tried everything.

I updated drivers, tried to change power managment settings (another thing that I dont understand is why am I missing all those advanced power options in Windows 10 Home), tried to turn off different options in BIOS, checked charger voltage but nothing helped.

While I was searching for solution I tried to install Dell Support Assist. Since I was without internet SupportAssist installer stuck on regular screen that installation is cancelled. I have had game open and I noticed that it is not lagging now. I closed Support Assist screen and it started lagging again. I opened it again and it stopped lagging. I am very confused but I believe now it is some kind of software problem which I cant understand.

Can anyone please help me with this?

Thanks!