Reddit mentions of Energenie ENER011 Power Management System

I don't do automatic power-down but it would certainly be possible. I have manual control integrated in to OctoPrint's UI, though.

As I'm in the UK, I have an Energenie ENER011 USB-controlled trailing socket, connected to my rPi by USB. It's compatible with the sispmctl tool to control its soft-switched sockets. This is the real magic which does the scary "controlling mains power" thing.

I have a couple of simple Python scripts to turn the printer power sockets on and off (just wrapping the invocation of sispmctl - not really necessary), then I used a little part of this guide to add entries in to the "power menu" of OctoPrint.

Writing your own plugins for OctoPrint is not insanely difficult, if you can forego making it configurable from within the OctoPrint UI (as that adds a bunch of extra work) or worrying too much about making it polished for distribution in the Plugin Repo (ditto). Remember to give yourself a way to switch the printer power back ON easily, too!

The tricky thing may be finding a "sispmctl-compatible" USB smart socket, if you're not in the UK (and hence can't use that one). I guess if you were in another 220v-50Hz place, you could get that UK-format one I linked above, replace the mains plug and use a travel-adaptor (or use a UK IEC lead) to connect the printer power.

Others have done clever hackery with using off the shelf RF-remote controlled mains sockets, either wiring the original transmitter up to a Pi to fake button-pushes, or using RF hardware to sniff-and-spoof the signals. There are general tutorials around for those approaches if you google for something like "switch mains power with raspberry pi". I don't blame you for wanting to keep mains power at arms length - as you can see, I did too!