I'm replacing a Dell laptop power supply with an old Mac Mini supply I have laying around. The broken Dell psu outputs 19.5V and 4.6A and the Mac psu supplies 18.5V and 4.6A. I hoping that's close enough and will suffice.

My issue is splicing the Dell cord onto the Mac cord coming out of the Mac psu. The Mac cord simply has a red wire and a black wire, as seen here:
enter image description here

The Dell cord has the outer layer of black rubber, then a layer of wire mesh, surrounding a layer of white rubber, then another layer of wire mesh, then another layer of white rubber, and lastly a thin wire in the middle. Here's a picture. The two wire mesh layers are twisted up.
enter image description here

My question is which is negative and which is positive? Here's a picture of the Dell connector:
enter image description here


  • \$\begingroup\$ Solved and updated here: reddit.com/r/AskEngineers/comments/x1eye/… \$\endgroup\$ – paulwal222 Jul 24 '12 at 2:49
  • \$\begingroup\$ that is almost the same answer you got here except that the user did not specify which is + and which is neutral, the outside is the standard for neutral. Really want a multimeter yourself to be sure. \$\endgroup\$ – Kortuk Jul 24 '12 at 8:31

You cannot mate this connector with a two wire PSU. This connector has three terminals: The metallic surface outside, the surface inside and the pin. The laptop uses this pin to detect the type of PSU it is connected to - otherwise it will not use external power.

You really should buy a replacement from Dell.

  • \$\begingroup\$ I just realized that the Mac cord has three terminals as well. Will that work? You can see the grey wire perpendicular to the red wire in this photo: i.imgur.com/xpNpuh.jpg \$\endgroup\$ – paulwal222 Jul 23 '12 at 22:17
  • \$\begingroup\$ The third wire is there specifically to authenticate the power supply and thus force you to buy the OEM one (standard corporate scumbaggery). \$\endgroup\$ – jms Jan 26 '16 at 18:03
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    \$\begingroup\$ @Turbo J: I think 'otherwise it will not use external power' is incorrect. It will use external power but won't charge the battery as far as I know. \$\endgroup\$ – Transistor Jan 26 '16 at 18:06
  • \$\begingroup\$ @transistor Interesting, I didn't know that. Why would they allow you to run the laptop but not charge it? \$\endgroup\$ – jms Jan 26 '16 at 18:08
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    \$\begingroup\$ The conspiracy loonies will say it's to boost profits. As Daniel said, they're using the 1-wire protocol to pass voltage and max current capability to the laptop. If the PSU is powerful enough charging is enabled. See this Hackaday article which has broken links to the real article. :/ \$\endgroup\$ – Transistor Jan 26 '16 at 18:17

Have a multimeter? Check which terminals are positive and ground and connect them. Dell does use a 3rd wire which operates on the 1-wire protocol to send an electronic signature to the computer which allows the battery to charge. I'm not sure if apple chargers use the same thing or not.



Well the white is the sense and that will make laptop know that the right charger is connected , the open sheild cable is the power, when the big thick sheild is ground ,,, but you cant use 2 wire power instead ,,, you can use any other 3 wire board useing the same config in other power the sense can be blue like hp , or red , or grey its simple if you have a multimeter enter image description here


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