It is possible to build a power supply with dual polarity and current control using two of our kit 1138 (0-30 V / 0-2 A laboratory power supply).
Here is what you need to do.
If you want to make a dual power supply you will need to build the two kit 1138 separately. Each kit must have it's own transformer so you will have two individual PSU's.
After you have built the two PSU's you must connect the (-) of the first PSU to the (+) of the second. The connection between these two points will be the common (0) output of the dual PSU.
The (+) of the first PSU will be the positive line and the (-) of the second PSU will be the negative line.
You must adjust the voltage and the current with the separate potentiometers so that they are set at the same levels.