It would be hard to dispute that your Dell Inspiron 6400 AC Adapter may be the single most important piece of equipment you need. Without it, you wouldn't be able to use your computer after an hour or two. Dell AC adapter runs your computer and recharge the battery. Unfortunately, they do not last forever and the Dell Inspiron 6400 AC Adapter can be quite expensive to replace, so take care fo it.
If you've determined that the outlet is working, disconnect the Dell Inspiron 6400 AC Adapter from the computer and plug it directly into the wall, bypassing any power strips or surge protectors. Your brick, which is the black box in the middle of your cord, should have an LED light on it that, when powered, should turn green. If yours does not have an LED light, feel the brick for heat and vibrations that will tell if you if it is receiving a current.
The main reasons that the Dell Inspiron 6400 AC Adapter fail are damage to the power brick from dropping or jarring it, cord damage from pets or pests and damaging the cord by winding it or bending it repeatedly. You can extend the life of your Dell ac adapter by treating it gently, never pulling the cord to remove the plug from the wall and never pinching the cord in drawers, under furniture legs or in doors. Always keep your Dell Inspiron 6400 AC Adapter in a cool place and uncovered.
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Dell Inspiron 6400 AC Adapter Features/Specifications : (http://www.usadapter.com/Laptop-Dell-Adapter/Dell-Inspiron-6400-AC-Adapter.html )
Input: AC100-240V (worldwide use)
Output: DC19.5V 4.62A
Power: 90W

Connecter size:
Internal Diameter: 5.0mm
External Diameter: 7.4mm
With central pin inside

Keep your Dell laptop running at full power with the Dell Inspiron 6400 AC Adapter
Computer accessory powers your device while you are away from home
Computer hardware includes circuitry to prevent over- and under-charging
Internal fuse prevents damage from sudden spikes in voltage
Red LED indicator shows power status

See more information on: http://www.usadapter.com