Syncee can upload new products to your store if you have a proper file for this type of import.
If you choose this type of import, Syncee will not update the products, it will only upload the new ones each time when the task is run.
How to test it?
Do an upload task and upload one or two products.
Add more products to your test file.
Run it again and Syncee will upload just those products which are new in your list.