In general you will be absolutely fine. If you are worried, use the cable first on an exposed, nonflammable surface. Plug the device in and watch the cable carefully. If you can see it smoking or feel it heating up(even a little bit) you have a problem. Otherwise it is just fine to use. I've handled kilograms of random IEC cables over the years and never once run into one that works only in 110/120 volt countries. Still, I wouldn't run a cable I wasn't sure about under my favourite rug and/or house supply of gasoline soaked rags before testing it(especially when the test takes 2 seconds and a new IEC cable is maybe 3 dollars anyway).
About wire gauge. "Gauge" is just the term for the thickness of a wire. All else being equal, thicker cables can carry more current.