Possibly I am going to regret joining this thread, but...
Your statement makes no sense. How do you think a split supply works? This is a classic design used in various forms on production systems for decades. You are over-thinking this - just treat the power supply as a black box with +/0/- outputs and don't worry about where the current goes inside it, because you are getting confused. The + or - side can supply current and the return path is through the 0v line. They can supply current simultaneously and 0v absorbs the difference. Don't mix PSU design into your switching requirements until you've done the rest and decided the PSU needs to be somehow special.