Walmart power adapter voltage increase if in-between two settings?

[realflow100]

I was adjusting the voltage from the adapter that I have (2 of them actually) its adjustable between 3v 5v 6v 6.5v 7v and finally 7.5v

But all of a sudden when I was monitoring the voltage it jumped up to 11.5v when the switch is between 7v and 7.5v!! Yikes!
I thought I fried it somehow but finishing my adjustment of the sliding switch to 7v registered just fine at around 7.1v (Not very accurate power adapter but voltage does drop under load to around normal value)

It also does the same thing between any other setting like 7v and 6.5v registers as 10.3v or so

 

[davenn]

(Not very accurate power adapter but voltage does drop under load to around normal value)

all the unregulated ones do ... they ALL will read a much higher voltage till a load is applied

 

[realflow100]

but what about the problem of reading 11.5v? I believe thats what caused the problem of our Roku becoming toast (noticed the power supply was on 3v so i switched it to 5v WHILE it was plugged in. not knowing it would do such a thing. and pop.. burnt smell.

but I still dont know what causes it to become higher voltage between its listed values. they are also very noisy power supplies. (tested using a speaker with 100uf capacitor in series and noticed a lot of static)

 

[(*steve*)]

I recommend setting the voltage before connecting the load.

The device is obviously not designed to maintain a sensible voltage when the switch is between positions.

 

[Colin Mitchell]

The circuit has been incorrectly designed and the voltage rises to full output voltage when the switch is not making contact.
If the switch wiggles when it is in the wall, your equipment will be damaged.

 

[realflow100]

should I replace them with brand new ones? they cost 35$ total so should i just skip trying to use them for any actual device and scrap them or use them for perhaps a diy project of some kind?

 

[Colin Mitchell]

Get one that doesn't jump up.

 

[realflow100]

should I get one that's at a fixed set voltage?

 

[Colin Mitchell]

If you can.

 

[cjdelphi]

It almost sounds like an lm317 and several resistor dividers like the attached image

Or it could be a transformer with multiple taps secondary side, but i'm not sure it would jump like that between positions

 

[realflow100]

We have 120v where we live. differing from your diagram. Its DC output ranges with a sliding switch from positions 3v 5v 6v 6.5v 7v and 7.5v but when its between 7 and 7.5 it goes up to 11.5-11.6v
and if its between 6.5v and 7v its 10.3-10.4v and so on.

Though it has very weak current output. and shuts itself off if the - and + are shorted or have too heavy of a load on them. (less current capability at higher voltage selected too.)

 

[Kiwi]

I was always told to disconnect the device, select and confirm voltage, and then reconnect as Steve suggested in #4.

Are you shifting these adaptors around between multiple devices?

I know it is initially a bit more expensive, but my suggestion would be to buy a suitable adaptor for each device, set it and forget it.
No matter how careful you are, sooner or later you will shove the wrong voltage into something.
Once the smoke leaks out it can be expensive to force it back in.