Hi Ben,
As with all DC Power supplies, Ground(-) is on the outside, Power(+) is on the inside of the plug.
The best way to use these WAPs is with Ruckus Power supply, that is usually around $10 give or take. 12V 1A should do the job. A PoE Injector will also work.
Do NOT use these with anything other than 12V PS. You can float the Amperage up to 1.5-2A, but do not change the voltage. You are risking to damage the device.
Cheers,
Alex