PSU+48V

design was on the web. It's not mine.

The 18 volt supplies are pretty much standard. The incoming 18V RMS AC is rectified at BR1 and smoothed by C1 & C2. CI1 and IC2 regulate down to ±18V, and C6-C9 help keep the regulator ICs stable.

The incoming AC signal is also fed to a second rectifier, BR2 via two electrolytic capacitors, C3 & C4. The rectified output is smoothed by C3. The 4 diodes in the bridge rectifier and the capacitors C3-C5 form a pair of Cockroft-Walton multipliers in parallel. This is easier to imagine of you picture C5 as two 100μF capacitors in parallel. Two diodes and two 100μF capacitors would comprise each parallel multiplier

The output is fed to the LM317 regulator, the voltage being set by resistors R1 & R2. D1 is present to prevent the output being held higher than the input by any electrolytic
caps that might be sat across the 48V line in whatever the circuit might feed.