9V adapter type

I have a device that specifies 9V input from a 500mA AD-16 compatible adapter. I don't have one. But I happen to have a Cambridge Soundworks TEAD-48 adapter that outputs 9VDC, 1A. Would I be asking for trouble if I used it instead?

Should be okay. Make sure to not swap + & - outputs with the + & - inputs.

It's got a 2.1mm plug. When I used it to power an Uno my DMM measured it at 11.9V. I imagine it's 9V at 1A.

Should I worry?

The old style "wall wart" power packs had a transformer, and the voltage drops substantially under load. So, the 9V at 500 mA would be the loaded specification. 11.9V unloaded would be fine for a device intended for that sort of power supply.

Modern adapters have switching regulators and their output does not vary much under load, up to some maximum current.

So if it is not regulated (which switchmode almost always are), the 1 A supply will give a higher voltage at the specified load than the 500 mA one will.

Whether this matters, is another question, depends on the particular "device".

I just noticed that the specifications also include the phrase "center minus plug". That's opposite what the SoundWorks plug has (and my Uno expects). I foolishly thought that all 2.1mm plugs would have the same polarity.

I could reverse the wires but I think I won't take the chance.

Thanks.

Yes, spend $5 and get a switching regulator wallwart:
http://www.dipmicro.com/store/index.php?act=viewCat&catId=690
I use the 7.5V units all the time to feed the barrel jack of regulator equipped Arduino's, and the 5V units for when I don't use an onboard regulator.

12V for driving strings of LEDs.

jboyton:
I foolishly thought that all 2.1mm plugs would have the same polarity.

But, at least, you noticed.
Assume nothing. Trust but verify.

jboyton:
I have a device that specifies 9V input from a 500mA AD-16 compatible adapter. I don't have one. But I happen to have a Cambridge Soundworks TEAD-48 adapter that outputs 9VDC, 1A. Would I be asking for trouble if I used it instead?

What device? This sounds like audio equipment in which case its important to avoid a switchmode supply
which might create lots of audible noise.

You hit the nail on the head: it's an "effects box" for a guitar. The 9V adapter costs $25 which is sort of too much for a $50 device. Fortunately it will also run on rechargeable AAs. Or a USB cable with mini connector. I think I'll just go get one of those cables.

I'm glad I hesitated. I almost just plugged it in. Do you think it would have survived?

No idea. It entirely depends on whether the "device" was specifically designed to survive such an insult. Applying more volts than it is designed for in reverse with more current available than specified is a pretty good test!

Manufacturers deliberately making products with non-standard connections, specifying "Use only the adapter provided with this equipment" is, well, common marketing practice, isn't it?


I am of course referring to the backward-wired (centre negative) power supply, not the other.

Note that the "normally-closed" contact on a coaxial power jack is on the outer. This is used to disconnect an internal battery when mains is used, but this was rarely a problem as the negative of the battery was not connected to anything else, though it becomes more tricky when the battery is rechargeable.