FRE 1101: "wide discretion" for sentencing judge
In a recent Fourth Circuit case (United States v. Slager, 912 F.3d 224, 237 (4th Cir.), cert. denied, 139 S. Ct. 2679, 204 L. Ed. 2d 1080 (2019)), the court reminded litigants in a footnote that judges exercise "wide discretion" in sentencing and that the rules of evidence do not apply in sentencing hearings:

See also FRE 1101(d)(3).
The Fourth Circuit was quoting a U.S. Supreme Court case, which Justice Sotomayor stated:
This Court has long recognized that sentencing judges “exercise a wide discretion” in the types of evidence they may consider when imposing sentence and that “[h]ighly relevant—if not essential—to [the] selection of an appropriate sentence is the possession of the fullest information possible concerning the defendant's life and characteristics.”
Pepper v. United States, 562 U.S. 476, 480, 131 S. Ct. 1229, 1235, 179 L. Ed. 2d 196 (2011)