HP Elitebook 6930P strange problem

Hello. recently my HP Elitebook 6930 is showing a problem. whenever my charger is connected its display flickers and when its removed its fine. it happens sometime. its own charger with which it came was damaged so bought another one original but used as new ones which are imported here are not original ones. I have created a video of my problem so you people understand it better

Video Link Here

and when i remove battery it works without any problem with same charger. What is causing this problem ?

if thread is in wrong section please feel free to move it.

 

thanks for the reply. ATI one HD 3450.

edit: its a really strange problem. it mostly happen at day time. sometimes not even a single time in night. here in my country at night voltage goes down a bit as compared to day.

 

and one more thing to add that its original charger was damaged about 3 months ago and i bought a used original one as new ones available are chinese made.

 

yes right. GPU temp is at 53C. what you think is may be the reason for this problem ?