Microwaves... I personally find something else more annoying, the power output is often regulated by a very crude PWM - so basically if your magnetron is rated for 1 kW, "500W" is effectively 30 seconds on, 30 seconds off, or 15 seconds on, 15 seconds off, 15 seconds on and 15 seconds off. Or whatever ratio the microwave controller uses under the hood.

That's fine if you need something to be in the microwave for a few minutes, but it absolutely sucks if you need something to be close to (or much less than) the period time... it's completely random and depending where the prior usage started, how much active time your ingredients experience.