Broken AC Adapter?

I have a HP Compaq 6715s laptop. My adpater doesn’t seem to be working anymore – whenever I plug it in a warning comes up saying “Smart AC adapter power output is too low for this computer”. If I wiggle the cable that goes into the laptop around enough it eventually works, but only for a few minutes or until the angle of the plug is changed. It won’t charge or run on AC power — is there anything I can do? Or do I need to buy a new adapter?
Any help would be greatly appreciated.