Why does my laptop run slow when charging?

I just recently got this laptop it is a Lenovo G505s and when I plug it in, it runs very slow but there's no sign of extra CPU use in task manager. It is also the stock charger thank you

Was that charger original? If not, you'd better make sure it's the one that powerful enough. Gaming laptop usually need more power than others. If your charger could not provide enough power, it will slow your performance. I think that you need a new battery for the computer or you need to buy a new original charger.

The problem is not with charger. The problem is the setting. Go to control panel, click on Power option. Choose power plan and click on change plan settings then click on advanced power settings. And select the option on charging…

May be charger problem buy a new

Never came a cross such an issue… As you said its a stock charger yy don't you buy a original one and check