1 Symptoms are due to the effects of excess acetylcholine on nicotinic and muscarinic acetylcholine receptors in the CNS, at neuromuscular junctions, and in the sympathetic, and parasympathetic nervous systems. 2  Nicotinic and muscarinic receptors have different. 3  Functions.
We're taking here about mains voltage (say 120 V or 230 V AC) power supplies with power ranging from a few Watts to several hundred Watts. Switch mode power supplies are everywhere; here are some pictures of their guts. The big high power components and small heat sinks are typical of SMPS. These devices are incredibly reliable, but being very often left powered all the time (even when their load is switched off), they still are the weak link.
What I am getting at is you don't want to turn off the recirculating pump, or the house to warm up, and then get scalded when you turn on your tap water to wash your hands. (for instance, my hot water tank is set to like 130F at it's hottest to eliminate scalds.) Showers are not that hot like that though.