The power supply for the amplifier was chosen to be an unregulated supply of transformer->rectifier->reservoir capacitors topology. The amplifier will use symmetric (equally positive and negative) supply rails.
The standard diagram for an unregulated symmetric power supply is shown below:
Supply rails and transformer
For a single amplifier channel, driving 50W worth of power by sinusoidal output into an 8 ohm load requires an RMS-voltage of 
In order to allow for stereo stages plus preamp electronics, interface electronics, and to give some VA-headroom, a 225 VA toroid transformer was selected, at 230V primary, +-25V secondary.
Capacitor bank sizing
The relationship between the voltage of a capacitor and the current drawn from it is given by:
Assuming a constant current, we get:
At worst, for the case where we have a full output swing and where the output frequency is low enough that the output sits at the positive supply rail, we have an output current of roughly 35/8=4.4 A . The capacitors must continually source this current in between two of the rectified voltage peaks from the transformer, without dropping too much in voltage. Allowing for a worst case dip of 3 V on the supply line during this time period (1/100 s since the line connection is at 50Hz), we get a capacitance of:
Approximating this to standard sizes, a capacitor array of two 6800µF-caps on each supply-side should be sufficient.
Other components
For the rectifier bridge, I picked something sturdy that wouldn’t be bothered by the fairly large currents. It’s a KBPC-type bridge with a built-in heatsink, dimensioned for 30A.
I also added a slow-blow fuse at 3.15A on the primary side of the transformer.