Dilshan designed an offline high voltage AC power supply primarily for SMPS testing. It outputs a square wave, so hooking it up to a mains-transformer based linear supplies is not a good idea, as the transformer will overheat. It’s open source hardware, so the schematics and design files are available.
This is a high voltage, low current, offline, AC adjustable power supply for electronic/electrical experiments. This power supply is mainly design for switch mode power supply (SMPS) experiments and to drive basic high voltage electrical circuits. Thanks to the isolated step-up transformer this power supply breaks the ground loop and provides shock free – safer high voltage output. This offline (or isolation) feature preventing accidental current from reaching ground through a person’s body.