On my USB hub where the power supply plugs in, the polarity is unmarked (I got it used, from my brother's friend). I need to know what the polarity should be.

I don't think it makes a difference about the brand. Could someone who has a USB hub tell me what the polarity markings are?

  • This is why I need to know about the polarity: Usually the center pin is positive and the outer pin is negative. But I'm not sure with this, and want to be certain before I plug anything into it.
  • Could the mark be somewhere on the name plate? It should look similar to "- (o +". To check it, use an old usb cable, cut it thru, the red cable should show + and the black one should show -.
    – ott--
    May 16, 2012 at 14:21

1 Answer 1


Its true that the center pin is usually positive, but since you don't mention the model specifics, it could the other way around on yours. Rather than fry your hub, might be easier to take a volt meter set to Oms, and check which connector is ground. Touch a metal exterior to each connector. The ground connecor will show no resistance. If there isn't a metal exterior housing to touch, then opening it up is about the only way to find out what's inside a "black box".

  • 2
    Hmm, if it's continuity testing you're suggesting, how about testing against the positive/negative USB power pins? The USB pinout is well documented.
    – Bob
    May 16, 2012 at 13:45
  • Thanks jdh, that makes sense to use a volt meter to check, given lack of other information. I found the model number, it is a Macally Trihub 7 (or Trihub7). I checked online, found descriptions, but couldn't find documentation. Well, not any that had specifications like a real user's manual would. Might you know anything about Macally? May 17, 2012 at 7:26
  • Yay! It worked, polarity was positive on the center pin. I checked with a volt meter. And then I found a diagram online. I saw it before but didn't realize that if I hovered over it, the voltage would pop up. But it didn't tell me what the polarity was, I needed you for that @jdh Thanks again! May 17, 2012 at 9:49

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