I’ve posted a comment on the developers blog

Here:
https://www.emmanuelgeorjon.com/eg-delicious-sync-1791/

And here:
https://www.emmanuelgeorjon.com/en/eg-delicious-developpement-suspendu-3757/

Asking that they update the plugin for the new delicious – hopefully one day soon they’ll have time…

https://www.ads-software.com/extend/plugins/eg-delicious-sync/

If you link your Delicious account to your Yahoo! account you cannot login using a username and password. You have to use your Yahoo! credentials.