30 volt power supply
Not exactly on topic, but close.
I just got a kit from China for the electronics for a 30 volt 3 amp power supply. The voltage and current are adjustable. I bought it off AliExpress for $ 3.8x including shipping. No enclosure or transformer in the kit of parts.
If you look enough you can find a vendor on Ali that has a manual on line with the schematic. The pcb is 3.25 inch by 3.25 inch. The vendor I used is
FYD open source hardware