Mo. Rev. Stat. § 456.980: Governing Law — common law and principles of equity.

1. The creation, revocation, or amendment of the power is governed by the law of the donor's domicile at the relevant time, and the exercise, release, or disclaimer of the power, or the revocation or amendment of the exercise, release, or disclaimer of the power, is governed by the law of the powerholder's domicile at the relevant time.

2. The common law and principles of equity supplement sections 456.970 to 456.1135, except to the extent modified by such sections or other laws of this state.