Mains adapter (SPN 4079A) and voltage with no load

If the appliance requires a regulated adaptor, then it may well damage the appliance. What is the appliance? Someone might be able to say if it needs a regulated supply or if it includes it's own internal regulator, or doesn't care about having an unregulated supply.

Yes, it's an unregulated adaptor. It probably approximates rather more to a 17.3V power supply in series with a 12ohm resistor (which would drop the voltage to 12.5V at 400mA), but that's a rather simplistic model of an unregulated PSU.

Very likely with no load and not regulated.

You need to load it with a resistor so it draws the same sort of current as the unit you wish to run it with. And check again. If it's a very low current device, it may well still be too high. But a regulated 400mA 12 volt wall wart costs less than a tenner from Maplin, etc.

Once I was in a similar situation. If you can, connet the item to a 12 v car battery and measure the current draw.( the battery will have 12 to 13.5 v and provide whatever current is needed) Then if it is about 400ma then it would be ok to use the adaptor because anything drawing about that current will cause the voltage to drop to about 12-13 volts.( as per the specs of the adaptor). Ali Tonto

What you are seeing is quite normal for an unregulated adapter. Use it with a load of 300 to 400 mA and you'll get the right voltage.

Yes, but most devices have fluctuating amperage demands, thus max 400mA and when idle less.Only a pocket light will absorb a constant current.That's why regulated power supplies were invented.

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I had an adjustable power supply, from 1.5 to 12 V, which in 1.5 V outputed

7.2 V!Definitely get a regulated power supply they are not that expensive.I got an 6 V for a radio for less than 12 euro, or you can construct one, if you have got a soldering iron and can do a little soldering.email me for schematics.Devices like cell phones must be having their own regulation, because their power supply has only rectifiers.

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current.That's why

That's why circuitry that is very tolerant of wide voltage changes was invented. Especially considering that a battery operated radio might start out at 9V and have to operate clear down to 7 or 6V before it quits. It's just the nature of batteries.

whatever

Not true! *All* unregulated "wallwarts" have an output voltage higher than the "spec" even at full load. Measure some and find out for yourself.

And just exactly _what_ axiom do you base your unequivocal statement on?

All generalizations are false, including that one. I've found some that run low.

... However, there is a kernel of truth to what you say... the rated voltage tends to be treated as a minimum, so they're probably more likely to be high than low. But the ratings are very inexact.

Fact, supported by more measurements than you would want to do.

Plwase specify brand, make and model and/or where i could buy one of those wierdos.

One of the reasons they are so high, appears to be that they aer "designed" for 110VAC input, and power here in the US seems to be semi-universal 123VAC.

But Japan, as I understand it, is still 100V. I wonder if they are intended to work OK there even though nominally designed for America.