"Wert in the power of" is a phrase that expresses the idea of being under someone's control or in a vulnerable position. There are several synonyms that can be used to convey this same idea. For instance, the phrase "at the mercy of" suggests helplessness or vulnerability. Similarly, the expression "under the thumb of" or "under someone's heel" communicate the sense of being under someone's control or domination. One could also use the terms "under someone's sway" or "in someone's grip" to convey the same idea. These synonyms help to add nuance and variety to the expression "wert in the power of" and expand its usage in writing and conversation.