The efficiency of switch-mode power supplies impacts energy use, from the consumption of the smart-phones in our pockets, to the photovoltaics powering our grids. Pushing that efficiency beyond today's 98% has an important role to play in fighting climate change - and energy costs. While the last 40 years have brought many advances in semiconductors, there is an increasing need for investment to improve the capabilities and properties of magnetic materials too. Prof. Marco Jung talks to Dr. Peter Wallmeier, Senior Director R&D at Delta Energy Systems, about the issues in episode 4 of the"Sound On. Power On." podcast. They also discuss the important opportunity presented by the combination of reactive loading, renewable power sources and storage in alleviating the voltage and frequency deviations that result from the increasing stresses on our modern, complex and interconnected power grids.