Today I find a negative power supply units circuit on 9Volt sizes to give my friends. But the most circuit is positive voltage supplies only. Therefore I think will get back to the direction of the electricity to negative form. When use Transistor 2SC1061 or TIP31 as a result give current about 1A and Transformer must have 1Amp size with.
Now we change with TIP42 PNP transistor type and switch polarity of Zener diode, Electrolytic capacitors, and more other parts same one.
but you want to builds easily maybe use IC-7909 dc regulators or look at other circuits here.