Is it possible to connect a dishwasher or washing machine that is not smart itself through a smart plug to Homey and also to Tibber, so that it can be controlled based on low energy rates?
As long as it continues the preferred program after the mains is cut for x hours, yes.
I control my non-smart dishwasher and tumble dryer like that: first start the preferred program, wait for the machine to actually start, then turn off the smart plug right away.
Have Homey turn it on at the lowest energy rates using Tibber prices.
There also exists button/devices that can actually push buttons on the diswasher.
I have seen users on this forum (way back) using those for coffeemachines etc.
Not sure what the were called, but those click-buttons could pottentionally turn the dishwasher on/off and even set the right mode/program.
Yes @Undertaker, thats the one i ment!
I use a smartplug with metering for my washer machine,it works very well