I'm not a lawyer (I just read regulations for fun). My understanding is Congress can still explicitly delegate authority to agencies, but an ambiguity in the law is no longer treated as an implicit delegation of authority.

As an example, the authority to define foods is explicitly delegated by Congress.

https://www.law.cornell.edu/uscode/text/21/341

> Whenever in the judgment of the Secretary such action will promote honesty and fair dealing in the interest of consumers, he shall promulgate regulations fixing and establishing for any food, under its common or usual name so far as practicable, a reasonable definition and standard of identity, a reasonable standard of quality, or reasonable standards of fill of container.