In Switzerland, the planned transformation of the energy system creates a need for grid expansions. However, grid expansion projects often confront social acceptance issues. The public prefers high-voltage power lines (HVPLs) to be buried underground. Despite the perceived advantages of undergrounding, underground HVPLs can leave visible traces on the surface and are accompanied by electromagnetic field emissions. Given the importance of visual and health impacts on public acceptance of HVPLs, the present study investigates whether providing people with relevant information on these aspects of undergrounding influences people's perception. The results show that, after receiving this information, participants viewed underground HVPLs with lower acceptance, lower perceived benefits, higher perceived risks, and less positive feelings. Although public acceptance remained higher for underground HVPLs compared with overhead HVPLs, our study reveals that information provision reduces perceived differences between the two technologies. Furthermore, our results show that affective reactions to underground HVPLs have an indirect effect on public acceptance. We conclude that providing people with relevant information on possible drawbacks related to undergrounding is a necessary precondition for informed decision-making in the context of grid expansions.