How important are Volts and Ampere on AC adapters?

[Erva]

Hi,

I'm looking for an AC adapter for a device of mine that wants 17V and 2A. Do I have to get an adapter with exactly 17V, or would I be fine with 18V?

And does having more ampere than needed matter? If I had 4A on the adapter, would the device only use its 2A and be fine?

 

[Fardringle]

It depends on the device. Some can handle a voltage range, some need exact ratings.

 

[Number1]

The device will only draw the amps it needs, you should match the voltage closely and be mindful if it is AC or DC and the polarity of the adapter if it is DC.

 

[Erva]

OK, thanks. It says "DC Power" on the device itself, but I don't know how to check for polarity. I think I'll have to go to a store and ask about that.

Edit: it's negative, I found the symbol.

 

[JAG87]

Just so you know, non-stabilized AC adapters (the common wall bricks), never put out the exact rated voltage. A 12V adapter actually puts out around 17V, because under load it decreases quite a bit to around 13V. So beware that an 18V adapter might put out 23-24V under no-load, and if you are buying a very over-dimensioned adapter (i.e. 4A for a 2A load), the voltage may not go down to 18V.

Depending on how important and sensitive your device is, you may want to measure the output with a volt-meter before you plug it in.