This results from your spreadsheet software automatically recognizing the UPCs as a long number. Thus, it saves it in scientific notation.
Example: 12345678901 shows as 1.23E+10
To fix this, you can either:
Select the cells with scientific notation, right-click->Format Cells->Select Text and click “OK”
You can also highlight the UPC column, and then select “General” from the format box dropdown on the “Home” tab of Excel:
Here are some additional articles you may find useful: