Multilateral development banks (MDBs) play a crucial role in financing sustainable power infrastructure in developing countries. Yet, their clean energy investment patterns and levels of decarbonisation have varied significantly. While MDBs have formally aligned to the Paris Agreement, a comprehensive analysis of their power generation portfolios in the years post-Paris is missing. Drawing on two novel datasets of MDB activities and policies between 2006 and 2020, we find that MDB investments in fossil fuels have declined, reflecting progress in decarbonization. However, despite MDBs' alignment to global climate goals, we observe a stagnation of renewable investments and thus a significant reduction in overall power generation investments from MDBs, that is particularly pronounced in low-income countries. We identify differences within institutional features, policy enactment as well as recipient countries and technology-driven project characteristics contributing to this phenomenon. The findings raise concerns about MDBs' ability to scale up clean energy investments, ensuring their continued alignment with global climate goals following the phase-out of fossil fuels. This challenge is particularly pressing in developing countries, MDBs' primary clients, where the energy investment gap continues to grow.