Comma before the subordinating conjunction "when"

The Chicago Manual Style states that if the dependent clause is merely supplementary or parenthetical (i.e.,
nonrestrictive, or not essential to the meaning of the main clause), it should be preceded by a comma.

For instance,

At last she arrived, when the food was cold.

As such will "when" be preceded by a comma in the following sentence, or is the comma unnecessary?

And Mrs. Lynde says you can never be sure of getting good baking powder nowadays when everything is so adulterated.