Output 4 to 22 volts.

Variable-output power supplies have been around for many years.

The voltage is selected with a switch -- the supply doesn't "know" what voltage is needed.

I've never seen one with continuously variable output.

"micky"

** Such unit are SMPS = Switch Mode Power Supplies. ** It doesn't know.

YOU have to know and set the adjustments appropriately.

Makes them a real hazard to use.

** SMPS are not battery chargers.

.... Phil

** SMPS are not battery chargers.

They are if the device is charged from its AC adapter.

I have a number of SMPS chargers, for cell phones, juke boxes, camera batteries, etc.

"William Sommerwanker = TROLL "

** A * Power Supply * is not a battery charger. ** No.

You have a number of SM battery chargers.

Wanker.

... Phil

But, there is no supervisor circuitry in them, the power supply, which is what you have only supplies the raw power needed for both the device and the charging circuit inside the device.

You and I may get some flake over that one :)

Jamie

A battery charger is a specialized type of power supply. It is intended to deliver "power" to rechargeable batteries.

"William Sommerwanker"

** Massive red herring and straw man fallacy.

Plus a blatant context shift.

Wot a desperate wanker.

I have several universal ones here from Kensington. They made them in

70 watt and 115 watt versions. The 115 watt one has input cords for 120VAC, 12VDC (car lighter adaper), and a rather funky round one for (I believe 24VDC) airplane supply. The output cable has a 5 pin connector and there are a number of output adapters. A little experimenting showed the output adapter sets the output voltage and current limiting. Opening one up revealed three resistors, used to set those parameters.

There are a couple of ways a supply can avoid sending an overvoltage to a device. A fuse in the output and hoping the device has diode protection would be one. While it would be possible to manufacture a supply which ramps the voltage up until it hits a reasonable current draw, it isn't very practical.

PlainBill

Here's the wall wart:

Dynex - Universal AC/DC Power Adapter dx-ac501 "Converts 120V AC to 3-12V DC With 500mA maximum output. For 3V, 4.5V, 6V, 7.5V, 9V and 12V power."

The picture only shows 3 sides of the thing, I'll open the box next time I'm at BestBuy, to see if there are any switchers on the other 3 sides. .

For the laptop adapter, I looked some more and found

It turns out there are interchangeable tips that each connect to the power supply, and in each tip is a resistor. The wire from the PSU has 3 wires and a shield in it, and if one connects the grey wire to the yellow or the shield via a resistor, the value of the resistor and whether one ues the yellow or the shield determines the output voltage.

So you're right. It's told what voltage to make, although not so much by a switch but by a resistor value in the tip.

Thanks for the help.

Well, I don't know that it's really continuous. The text above suggests that the wall wart can have 6 different outputs. And the laptop power supply can have 30 different voltages, though I'm sure not every one has a tip that yields it.

--
It has a voltage selector switch. 

Go to: 

http://www.dynexproducts.com/products/cables-cords-adapters/DX-AC501.html 

and click on "English" under "DOCUMENTATION"

No, I guess not. I am used to replaceable tips, but didn't expect the tip to control the voltage.

At least with the laptop power supply, I have to use the right tip.

Well, it seems Targus got around that, in this universal power supply, which is no longer made. I forget what they make now, and I don't know how other manufacturers set the voltage.

Well, they do charge the battery of the laptop.

"micky"

** There is a charge regulator inside the laptop - f****it.

Wot a tool.

.... Phil

That doesn't change anything. Kerplunk.