On Tue, 28 Feb 2012 20:52:14 +0000, Andy Burns wrote:

> Beagle wrote:
>
>> Have a Avantalk headset that charges via USB. Have various phones that
>> charge by USB but also have a "mains adapter" such as this
>> http://www.ebay.co.uk/itm/190595261689 where the USB plugs in to the
>> mains plug.
>>
>> Assuming I can find one with the right output (5v 400ma), any reason I
>> can't use it for the headset?
>
> should be OK, it's generally the devices with higher e.g. 1000mA rapid
> charging that use special signals between charger and device to indicate
> higher power is available
>
>> Also, as 5v 500ma is as common as muck would it be ok to use or would
>> that 100ma be too much?
>
> It will only take what it wants, it won't get more "pushed" at it by the
> power supply, e.g. when you plug a 40W bedside lamp into a 13A socket it
> doesn't run at 3kW!

This reminds me of the time when our house still had 15A round-pin
sockets, and I was making an adaptor lead to a flying 13A socket. I
asked my physics master where I could get a suitable resistor to carry
the extra 2 amps (120 ohm, 480 watts...).
[ This was a very long time ago. ]