I have an LED light bar powered by 6 AA batteries connected in series. There is also an RF control unit to turn the light on/off. The light eats through the batteries rather quickly thus I decided to experiment attaching a DC adapter to the light.
Due to the way the batteries are connected, I assumed that the light takes 9V to power, so to test my theory I grabbed a used 9V cell and it worked perfectly - even responds to the RF remote.
I then grabbed several DC adapters that output 9V with varying current and then began testing to see which one will work. First I tried one with 200mA and the lights turn on, but does not respond to the remote control. I then upped the current to 300mA with same result, but when I tried it with 600mA I heard the dreadful "buzz" as soon as I connected the circuit (did not even turn on the switch). As expected, I fried the RF receiver module in the light - yet the light still works. Even going back to the 9V battery does not allow the light to be operated by the RF remote.
So now I'm trying to find out what happened. If I have the voltage correct, shouldn't the worse that could happen is under-powering the light due to insufficient current? I'm assuming that even if I increased the current, there shouldn't be a problem since the resistors in the circuit should be limiting the current so there shouldn't be a risk of burning something out. The only thing I can come up with is that the adapter was putting out way more than 9V to fry the RF receiver circuit. Are there other possibilities about what could've went wrong?