Using 2 postive regulators with 2 prong power supplies for bipolor power supply
If you view the output of a black box that has two wires coming out from a power source inside, one ++ and the other -- you would never know if it was a negative or positive regulator. In addition any current flowing out the ++ has to flow back in the -- wire when a load is connected between the two. All just depends on what you bring out as GND. 

So as long as the wall warts that you use have:


100% isolation between the input AC terminals and the DC outputs
No connections to the AC side safety GND


You can use the two wall warts along side each other, one as the +V supply and the other as the -V supply. Just tie the opposite sides of each together to become the DC circuit GND.