First I would use more than one test method to check the power at the USB. one of the small USB toys they have. Plus a voltmeter ,I would test the voltmeter on something if I wasnt sure about it.
I have read on the web where a user who damaged the power on a USB port, was able to use a good quality 4 port powered hub. In that situation the rest of the port was still functional, and he/she was able to use the port for something.
I would try that method of the powered hub , in hopes of knowing more, and to be sure that it would work if I supplied power there to begin with. The hub could be powered with batteries for any portable use still.
There are other devices which require no power from that port, they could be used to test also.
next I would analise how much I had to lose , and go for it. if the connection one way is actually busted, it isnt very likely to to head back into the computer any ammount that would mater. Proper polarity and isolation of the added power would be important, if your getting the power from the the same computer, even if converted with a DC-DC or a voltage regulation. Out of pure fear, and just general good electronics, the power going in there would be limited to ~.5A , using a mini fuse or tiny curcuit breaker, or via the max output of the regulation.
It still would be better to know what device this is, or anything else about it.