Capacitive power supply circuits been used for decades in things like alarm clocks, small appliances (coffee makers) and the like. They work pretty well for small constant loads without the bulk of a heavy transformer.
However, they are scary to work on and need special considerations for user safety.
Do not think about using one unless you really know and understand what you are doing.
Even an experienced engineer like myself will shy away from them, designing everything to the right of the bridge using a bench supply till everything else is proven functional before plugging in the AC with my other hand in my back pocket.