I know you just did a double take when looking at this power supply, what's up with the two cables? Normally you have a switching power supply that plugs into the wall and provides something like 5V or 9V or 12V regulated DC. This split power supply is interesting in that it gives you two power supplies! One is a positive-with-respect-to-ground +12VDC. The other is negative-with-respect-to-ground -12VDC. The max voltage differential is 24V from negative to positive so you are getting a true 'split supply'
Excellent for use with analog electronics, motor controllers, lab equiptment, modular synthesizers, or anything else where you've found yourself puzzling over the need for a matching negative power supply.
The black wire is your every day classic +12VDC with center positive. The white wire is the negative supply, its also center positive which means the center is the same as the black wire's ground. The 'ring' of the white-cable connector is -12VDC. You can draw about 500mA from each side, a total of 1A. Please note that the output is not as strictly regulated as some other power adapters you may have used, the floating voltage can be +-13V and at max draw, droop down to +-11V or so. You may want to have an extra linear regulator if you want the output to stay rock-solid over a wide current-draw range.