Actually, a toaster is more dangerous than a low voltage bench supply if you use it in the maximally moronic way. If you ask me to set a fire on purpose, and give me a choice of which to use, I'll pick the toaster. And, by the way, I don't buy the idea that people "instinctively" understand fire.

But the other, more relevant part is that a toaster or a washing machine is used for a single purpose in a stereotyped way. There are a bounded number of fairly well understood mistakes that people are likely to make frequently. You can list them.

A bench supply, like many other tools, can be used in an almost infinite number of ways, which you are meant to be designing for yourself. If you buy a washing machine, you're "saying" that you want to wash clothes. If you buy a variable power supply, you're "saying" that you want to design or repair electronics that might do anything, or do electroplating, or who-knows-what-else. There is no complete list.

You cannot do such things safely without actually understanding how they work, in more depth than an instruction manual is going to be able to give you, even if the manual somehow knew what you were planning to do, which of course it doesn't. You can't design an electronic circuit, or a plating protocol, and you definitely can't troubleshoot either one, without having a clue about Ohm's law.

People sometimes have their own ideas, based on actual understanding of something significant, and they need general purpose tools to support those ideas.

> The saw analogy isn't a good one - saws work within the range of physics that humans have instinctual understanding of. We instinctively know what causes a table to wobble.

... and yet people will try to build a table by attaching each leg with a single nail in the end, because they don't instinctively understand wood grain, or that there are lateral forces and leverage involved. The saw manual doesn't get into those things either. That's woodworking knowledge you're meant to have before you buy the saw. Even though you could easily put something heavy on the table and get hurt when it collapses.

Saw instructions are restricted to the actual process of sawing. They don't get into table design, not even the "inobvious" parts. Actually, many power saw instructions don't even say much about how to saw. They tell you how to mount the blade, and what this or that switch does. After the endless warnings.

> But what people should know and what they actually know are often very different.

I could also say that people don't read manuals. Especially not if the manuals are gigantic tomes, which is where they end up when they go in the direction you're talking about. The manual for your average power tool has pages of fine-print warnings, basically trying to explicitly forbid every stupid way somebody has misused that kind of tool in the past. Essentially no users read them.

I have an air nailer whose instructions helpfully inform me that I shouldn't use acetylene instead of air. It specifically says that. That's like toaster instructions warning you not to make your toast out of asbestos panels dusted with cyanide.

Hooking your nailer up to acetylene is not an obvious mistake to make. It's not an idea that comes to mind. It probably wouldn't even work well (before the fireworks started). It's not easy, either. You'd have to kludge up some weird adapter system to make the deliberately incompatible fittings work. Anybody who works around acetylene knows really well why it's fucking suicidally stupid. And, yes, if you don't know that, you shouldn't be messing with acetylene. Or nailers.

But apparently some cretin did it one time, and now it's in the instructions. Even so, the instructions for that nailer don't say that it's not for styrofoam. Which is more the sort of thing that was going on with the power supply. I guess nobody's lost an eye to a ballistic nail that came through a piece of styrofoam yet. Or at least nobody's had the gall to stand in a courtroom and say it was the nailer company's fault.

The cretin with the acetylene wouldn't have read the warnings, and now that they're longer, the next cretin is even less likely to read them. In fact, nobody expects most users to read the warnings. The warnings are not there to improve safety. They're purely for defense against lawsuits. They might even work for that, but they're not what you'd write if you actually set out to improve safety.

The real safety impact , if any, is almost certainly negative. Warning about obviously off the wall idiotic behavior overwhelm any actually useful warnings, and prevent them from being seen. On the other end of the spectrum, overcautious warnings, if they are read, breed contempt for warnings about really important, possibly inobvious risks. More is not better.

... and bringing it back to reviews and that power supply, such supplies typically come with a specification sheet and either no instructions, or one page with a few bullet points that would make no sense if you didn't understand how voltage and current relate. So even if the documentation on that particular supply were in some sense inadequate, it would still be up to the standards of any other supply you might buy. And in any case, the reviewer's claim was that there was something wrong with the device itself because it didn't do something the reviewer should have known was impossible. That's not a useful review.

However, the rounding issue is a big deal both in how people rate stuff and how they interpret the scores to the point where small numbers of responses become very arbitrary.