Can localized weather shocks to upstream fuel suppliers undermine down-stream electricity reliability? Using administrative data linking South African power plants to contracted coal mines from 2015 to 2024, we combine plant operating records, mining-firm revenue data, and route-level traffic sensor data. Exploiting within-plant variation in supplier-mine rainfall, we find that rainfall shocks reduce mine output and lower coal plant availability. Daily traffic data confirm that rainfall reduces coal deliveries along contracted mine-to-plant routes. These disruptions propagate to the grid, contributing to rolling blackouts. Electricity security hinges on the resilience of coal supplyn contracts and logistics, not only on plant resilience.