Trying to open smb://username@host/Downloads/ in Krusader or Konqueror offers to input the user password, but the user on Windows I'm trying to connect to does not have a password. Leaving it blank does not help, it still asks for a password.
Mounting via cifs works for me:
sudo mount //host/Downloads /mnt -t cifs -o username=username,sec=ntlm
It asks for password, but I can leave it blank and everything just works.
Using smbclient works too. It asks for a password, I leave it blank and it proceeds.
smbclient //host/Downloads -U username

How to achieve the same in gui?

Do you use Kwallet? I don't have that problem and I use Kwallet.