I'm hanging a 18.5lb chandelier, there is already a metal box in the ceiling from an old ceiling fan installed by the previous homeowners, the box is attached to a ceiling joist as required, however, it's not centered above my dining room table, I want to add a swag hook a few feet away so my new chandelier can be centered, is a toggle bolt in ceiling drywall on a sloped ceiling strong enough to support the swag hook and 18.5lb chandelier?
The toggle bolt will probably hold up just fine with a 20 lb. weight, but I can't say the same for the drywall itself.
Even if the drywall seems to hold for a while, do not trust it by hanging a 20 pound weight over your loved ones' heads like this.
You will want to install something solid in the ceiling to attach to. A piece of blocking between ceiling joists, or a hanger designed for the job.