I saw hurz posted a very complex single rail to split rail power supply converter and I thought we should first start from the basics. One of the disadvantages of these kind of circuits is that when you split the rail you also split the voltage two so if you have a 40V tramsformer you can get only 20V and if you want it regulated even less (yes im not forgetting the x1.4 voltage increase from the capacitors but even with them if you tax it out you still wont get 20V at the output). Usually this circuit could be constructed by only a few diodes but the power transistors are for current amplification so you can get more thwn 20-30mA at the output. Another disadvantage id that when you detach one of the loads the other one becomes inert too. To compensate you must short one of the emitters depending on which load you've removed
