polarity of dc power require by electronic device
Usually the center pin of a Power jack will be + / positive. I say usually because there are exceptions, every manufacturer can do as they please.

There is way to confirm the polarity though althoug I cannot guarantee that it will always be 100% correct. But on most devices the shielding of other connectors will be connected to ground. Also many times the metal chassis of the device will be connected to ground. Using a multimeter you can check which pin of the Power jack has the lowest resistance to these ground points. That pin then has a high chance of being the ground pin.

Some devices might have a reverse polarity protection diode. You can also test this with a proper multimeter on diode test. The diode must of course not conduct when power is applied with the proper polarity.