Perhaps the polarity of the two power adapters are different. Another possibility is one is DC (standard wall-wart) and the other is AC. Generally, using a 12V supply for a 13.5V system would either work or not work, but it would not "mess up" your speakers.
(An automobile battery has a nominal voltage of 12V, and many automotive adapters provide 12V. Yet the actual voltage of an automobile battery is closer to 13.2V.)
Check if the polarity was reversed or if you swapped DC - AC. You may have just bent the jack. If you reversed the polarity, you may have shorted a protection diode. If you have the equipment and background, it should be easy to troubleshoot.
Good luck!
Edit: A power supply can not provide "too much amperage"; current is a function of load resistance. A load draws current; the power supply does not "push" it. Read the amp rating of an automobile battery and ask why you can plug a 0.5 amp device into the cigarette lighter!