Repair or Replace
Another reason a Dell notebook power supply light goes out is often due to a broken cable. This can happen as a result of frequent moving around of the laptop with the power cable attached. The flexing and twisting will, over time, cause the cable to chafe and break. An easy fix is to strip the plastic covering where the break is, and twist the ends back together. To identify where the break is, feel along the cable for a lump, a gap, or where there is less resistance when the cable is twisted.
Tip: The break usually occurs close to where the cord is plugged into the back of the laptop.
You must be careful to cover the stripped wires with electrical tape, epoxy or a similar nonconductive adhesive after you fix the break, taking special care to ensure that the two wires (in the power cord) never come in contact with each other.
Another possible cause of a power supply failure is a blown fuse, but because laptop power supplies are well sealed and are often difficult to open and reseal, it may be better to simply purchase a new power supply. New power supply replacements can be found on eBay for less than $12 in many instances, with the possibility of you finding a used one for much less a strong possibility.