Where does the power of eminent domain come from?

Fifth Amendment to the United States Constitution
The "Takings Clause"

"No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a grand jury, except in cases arising in the land or naval forces, or in the militia, when in actual service in time of war or public danger; nor shall any person be subject for the same offense to be twice put in jeopardy of life or limb; nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use, without just compensation."

Article 1 Section 13 of the Wisconsin Constitution

"Public property for private use. The property of no person shall be taken for public use without just compensation therefor."