By default, your Supplier Exchange import task is on Upsert. It means that Syncee will upload new products and update products in your store which you uploaded previously from the same supplier.
However, this means if the supplier adds new products to the feed, Syncee will upload them automatically if you schedule the import task.
If you do not want this to happen, log in to your Syncee dashboard and select My tasks.
Click on the Edit button next to the task you would like to modify or simply click on the name of the task and go to the Summary page.
Click on the Task Type and choose update instead of Upsert of Import.