Laptop capt performance if I charge it during this?

I realized that today when I was playing league. Without charging the laptop, I had normal fps of 110-130, but as soon as I want to charge it while I'm in the game, it starts to lag. But why? Shouldn't it even be the other way around?

I guess the laptop switches to economy mode to speed up charging. It is also possible that the charging power source is too weak to provide full power to the game and charging at the same time. Does he also switch the display lighting to a level darker? That would be a sign of economy.