How to go about turning on/off a coffee machine with an Arduino?
If you get in far enough to short out the button, you're in far enough to bring the button contacts out as wires, so you can use a much smaller relay to momentarily close them, just as you do when you push the button. That leaves the heavy power handling where it belongs, in the appliance that was designed to do that. Just close the switch for 1/2 second or so and let the coffee machine do its thing.