Non-gaming power consumption has been improved a little bit over other Turing cards, but the differences are too small to really matter. Previous-generation Pascal cards are slightly more efficient in those states, but again with negligible effects for real-life.
Gaming power consumption of the GTX 1660 Ti is where it becomes interesting. With only 135 W during gaming, power draw is very low and clearly improved over Pascal. Such low power draw ensures that any power supply will be able to run the GTX 1660 Ti.