UV380 goggles block most UV radiation—nearly 100% of UVB rays and 95% or more of UVA rays. For occasional skiing at lower-altitude resorts, they provide adequate protection and can be a reasonable choice if you're on a tight budget.
The catch is that UV380 allows some UVA rays in the 380-400nm wavelength range to pass through. At higher altitudes, UV radiation is 30-40% stronger, and snow reflects up to 80% of it back at you. That small gap in coverage becomes more meaningful on bright days at elevation, where your eyes face intense UV exposure from above and below.
If you ski mostly at lower mountains, go out just a few times a season, or are buying for a growing kid who'll need new goggles soon, UV380 can work. But if you ski regularly, at high-altitude resorts, or on sunny spring days, UV400 is the safer investment. Never assume a dark lens compensates—UV is invisible, and tint has nothing to do with protection.