Beginner question on External Product ID (e.g. UPC)

Hi,

I am totally a newbie, I am trying to sell my first product, which is some computer devices purchased through Alibaba.

I have a question on External Product ID (e.g. UPC).

I am learning with this video instruction, https://www.youtube.com/watch?v=oH7gllwI80I, and it recommends getting a UPC code via GS1.org.

I have no objection to purchasing UPC codes on the site, but first I have a couple conceptual questions.

The product I purchased from Alibaba has been manufactured in China and already has a bar code and corresponding numeric code in the back of the box. Is it not somehow an external product id? If not and therefore I buy a UPC code for this product, would these two codes confuse the Amazon system (or anything down the path)?

Thanks a lot!