A power conditioner with voltage regulation keeps its output at a fixed voltage of 120V for a range of input voltage conditions. There is normally a minimum and maximum voltage within which the regulator can maintain a constant output voltage. These limits vary from manufacturer to manufacturer but 90-140V could be considered a general range.
If you need voltage regulation we recommend Torus Power's AVR and AVR2 models.
Nyal Mellor, Founder, Acoustic Frontiers