Load shedding used to be a very regular occurrence in Kathmandu to Pokhara (and I assume elsewhere in the country), but I understand it's been sorted out now. Turns out it was graft, and now they're supposed to be on near 24-hr electricity. That said, I always take a torch with me when I travel abroad, it's no fun being caught out with no light in unfamiliar surroundings, and power outages can occur in any country. Plus if you're going trekking, it's pretty much mandatory.
Cell phone led lights work decently well, and you'll have no problems charging electronics on many treks.