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Old 22nd Oct 2017, 3:37 pm   #14
merlinmaxwell
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Join Date: Jul 2008
Location: Maidenhead, Berkshire, UK.
Posts: 7,718
Default Re: Barrel type power plugs and sockets.

Those laptop ones have three connexions, +, - and a data pin. This uses the Dallas 'One Wire' protocol and is intended to make you buy a genuine replacement adaptor rather than overloading a generic type. I wouldn't mind so much if it was only the maximum current that was communicated, but, alas, it has to say "I am a genuine HP* supply" for example.
*other makes of laptops are available, mine is an HP.
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