Do I need a separate chime if I already have a video doorbell?

Only if you want an in-home audible alert that doesn't rely on your phone. Most smart video doorbells (Ring, eufy, Arlo, Tapo) send notifications to a phone app, but specialist subreddit threads and verified-purchase reviewers repeatedly note that phone notifications alone are easy to miss, especially in larger homes or for elderly users. A plug-in chime gives you a loud, house-filling ring without depending on a phone being nearby.