Don't know the exact reason, but now all three Yosemite Conservancy's webcams (Ahwahnee Meadow, Sentinel Dome and Turtleback Dome) photos are not being updated on the Yosemite Conversancy's website. The two webcams opearated by the Park Service (Turtleback Dome - Air Quality Western View and the Happy Isles Gaging Station) are still updating their photos. Don't know exactly what's going on.
If it was a power issue, I would suspect both Turtleback Dome webcams (the Park Service - facing west and the Yosemite Conservancy - facing east) would be inoperative at the same time.