D-Link des-3052
#upload cfg_toTFTP  x.x.x.x *.cfg(filename)
D-Link des-3550
#upload configuration  x.x.x.x filename
D-Link des-3220
#upload cfg_toTFTP x.x.x.x dest_file filename

Reference:http://madedream2.blogspot.com/2014/10/switch-config-file-backup.html