I decided to go with a fairly standard 7805/7905 supply with protection diodes, nothing really worth mentioning here.
[yes, I know four point cross connections on schematics are not in accordance to DIN schematic standards]
Nothing really worth mentioning with the construction either, other than that the electrolyte capacitors were wobbly so I hot glued them to the board to ensure they don’t eventually break off with oscillations from the transformer. The transformer is 2x 9V 315mA.
For the front connectors I choose Ø2,6mm Zwergstecker. The power switch is a soviet МТ-1Б.
The 7905 regulators seem to jump down to -6.5V without load, but applying a 20mA load brings them close to -5V. Interestingly this does not happen with the positive rail. (The LED is connected to the unregulated DC before the regulators, so both rails are without load)
I’m considering spray painting the front panels into some dull white color or so, because I really don’t like the polished aluminum look.