Germany here. I'd say from personal experience maybe once decade. That includes living in a village of ~3000 for eight years. One time I remember was caused by an excavator where it lasted several hours, the other instances were rather short.
I guess not having earthquakes, floods or hurricanes helps.
The other items at least in the US midwest would be ice storms (ice coating power lines making them heavy and branches getting too coated and falling on power lines) and thunderstorms (50+ mph wind coming through bringing down tree branches on to powerlines) or lightning strikes hitting power transformers.
It's a lot more common in Europe to have buried lines for anything after the high-voltage national backbone, so the grid is much less susceptible to weather.
Where I lived in Sweden, 30% of the network was already underground, but after a large storm in 2005 caused long-lasting power outages, they invested heavily and are now up to 70% underground.
I guess not having earthquakes, floods or hurricanes helps.