As JYelton mentioned in his post, you should not assume the polarity.
12V 𝌂 means that the adapter outputs 12V and the symbol next to it means "DC".
You can confirm the polarity by using a digital multimeter. One of the quality of a good digital multimeter is that it can display negative values. This feature is needed as you don't know the polarity.
Connect your adapter as pictured below. In the picture below, adapter's center conductor is being probed by positive (red) lead of the multimeter and the outer of the barrel is being probed by negative (black) lead.
If you get a reading with no minus sign on the meter then your inner conductor is positive and outer is negative. If your multimeter gets a negative reading or displays a minus, then the inner conductor is negative and outer is positive.
Make sure that the read lead goes to positive terminal and black to the negative terminal at the multimeter end.
If looking to buy a multimeter here is another post to refer to.
Another way to test the polarity is by using LED and resistor if you don't have a multimeter.
Wire up a LED + 1K ohm resistor like the image below:
Note the polarity of the LED; the flat side of the LED is negative. Polarity of resistor doesn't matter.
Now connect the other end of the resistor (top of the diagram) to the center conductor and the LED flat side wire to the outer conductor of your adapter.
If the LED glows then your center conductor is positive and outer is negative.
If LED doesn't glow reverse the wires. If LED glows in this case, then your center conductor is negative and outer is positive.
If LED still doesn't glow, check your wiring and your adapter.
If you have LED + resistor and no multimeter, you should get one.