You can use synchronization, if you need more flexibility.
It does transfer new files only, if you unselect all comparison criteria.
https://winscp.net/eng/docs/ui_synchronize#criteria

Also, I think "New" option isn't working because winscp tries to upload a file even if it already exists on the server.

Right now, these options are combined into a single checkbox called "New and updated files only", I'd be much more flexible if these two options have a separate checkbox each, sometimes files already exist in a server, but in different date than the currently uploaded one, I wish to ignore the date check on the file, but I couldn't in the current version.

Thank you.