New adapter not charging

Hello,
the original power adapter/charger for my dell inspiron 1520 is broken, so i got a new one on ebay. the company said it was the correct one after i talked to them a few times. My computer puts up a warning message saying the charger is not sufficient wattage, even though the guy insists that it is. He said i may need to update the BIOS, which i did but the problem is not solved. The charger was charging my battery, but now (after about a week) the charger does not charge the battery at all. I know the battery is not old, so it has to be the charger... any suggestions?