transformerless - How efficient is a capacitive power supply?

Something like this

Falstad sim version of it

(I'm tired, I keep making mistakes, so please excuse me for the second time.)

Now these are not very safe PSU's, due to the lack of isolation. But in sealed units, they can be a cheap way of getting the supply voltage for a microcontroller without an SMPS or transformer.

They are not 100% efficient due to the zener and resistors. But, I have several questions.

1. How does the capacitor step down the voltage, anyway? Does it waste power as heat?


2. If the zener were gone and the output was let to float around 50V, would it approach 100% efficiency?