Assume your second switch governs which lead from the power supply is +, and which is -ve.
Mighty important to get it right!
With the risk of getting it wrong or accidentally moving that switch.... I would question the wisdom of using that power supply at all!
Play it safe and use the purpose built power supply. Some are much more accurate than others, but you haven't said what is being powered up, and that may dictate what you can/cannot do.