I got PSU control working with a cheap tasmota smart plug and thought I'd share my settings for anyone interested.
Of course, replace 3dprinterrelay.iot.gravy.network
with the hostname of your relay. I recommend not giving it any internet access. You can password protect these calls if you are so inclined.
Switching Method: System Command
On System Command:
curl http://3dprinterrelay.iot.gravy.network/cm?cmnd=Power%20On
Off System Command: