Dell Latitude E6420 screen flickers with charger plugged in?

I just bought this laptop the other day refurbished from NewEgg, it was supposed to be a basic setup ( No DVD-R/W, BlueTooth, nVidia Graphics, Camera, Fax, the better resolution screen, etc). But lucky me they sent me one with all those features for the price of the basic model, my point being I REALLY don't want to send it back for a replacement so please try not to suggest it.

 When I first got it I checked the battery and charger to see if it was Dell brand but unfortunately they were replacements like I expected (but the charger is the right voltage). My problem is when I plugged it up to the charger to activate Windows and install updates, after which I started to turn down the brightness from the Fn / arrow keys and when I got to a certain level of brightness the screen went black, after unplugging it and a restart I plugged it in again and it did the same thing again without me touching anything. So for a couple days I just didn't use it while it was charging.

Today I decided to update the BIO's to the latest version incase that was the problem (from A5 to A21 or something like that) and that requires the charger to be connected so I did which gave me the same result, only this time I realized the screen wasn't off it was the backlight  that was off. So having to use a flashlight to see the screen I updated the BIO's and while it was updating the screen was visible again but after it restarted the screen still stayed on but was flickering (only with the charger plugged in).

I've tried adjusting the settings in the BIO's like I read somewhere to set the battery to default before doing the update but no change, haven't tried it after as I have it charging currently. Earlier I took the bottom cover off to check it out before any of this because the charging port on the laptop wiggled a bit (the whole thing not just the prong) and I found that the bracket which holds down the port was loose and tried tightening the screw but its down as far as it can go.

So my suspicions are either I need a certain driver update, the charging port was possibly replaced with a *** one, or the charger is just cheap Chinese junk but other than that everything looks appears like it did when it was new. Does anyone have any ideas as to what could be causing this?, I can take it apart and replace things myself.

It does have the nVidia NVS 200M if that helps

Any ideas?, Thanks.