Hi,
The notebook AC adapter will usually have the same warranty as your notebook, but contact your local ASUS support to confirm and discuss your options about getting it replaced, or check with your Best Buy store too if possible to find out how they can help with this (I'm not sure if they can, but wanted to mention it in case they have better options for you).
Let us know if you have any problems finding the correct contact information from the link below, but if you are in the U.S., you want to contact the retail line for notebooks purchased from Best Buy if you plan to call and be sure to have the serial number under the notebook ready.
http://support.asus.com/Hotlines.aspx?SLanguage=enAlso, if you don't mind telling us which notebook model you have, we can move you to the related section to get more opinions from other forum members with the same notebook model, otherwise, don't worry about it if you want to stay in this section.
Hope this helps and please let us know if you still have any questions or run into any problems arranging this.
Thanks.