I am looking to purchase a Dell E6420 14" i5 2.5 4gb 250gb with Touch Screen for our local police dept.  They will use this in the police car for their Computer dispatch software.  So it will need to connect to the vehicles dc system.  I know alot of 3rd parties pwr supplies cause the bios to go nuts and will not allow the battery to charge. So what dell dc adapter should I purchase.