Power transformers are crucial components in electrical grids, essential for the efficient transmission, distribution and management of energy. The design of power transformers must comply with international standards, including those set by the International Electrotechnical Commission (IEC), Institute of Electrical and Electronics Engineers (IEEE), and Eco-design regulations, to ensure optimal performance, energy efficiency, and environmental sustainability. These standards aim to minimise energy losses, enhance reliability, and reduce environmental impact throughout the transformer’s lifecycle. Transformer designers prioritise reducing losses, extending service life, and ensuring compliance with IEC standards, Eco-design criteria, or any other international standards specified by customers. In addition to these priorities, the cost and overall weight of the transformer are critical factors influencing the design process. This article compares IEC-compliant transformers with Eco-design transformers to evaluate energy efficiency, cost, and weight. This study conducted a detailed comparative analysis for three distinct transformer cases: 1600, 2000, and 2500 kVA power transformers. For each case, two transformer types were analysed: one designed to comply with the IEC standards and the other designed in accordance with the Eco-design Tier 2. The transformers were designed with cost minimisation as the primary focus, ensuring the lowest possible cost while still meeting the required standards. The study highlights the importance of clear, interpretable results for both researchers and transformer designers, enabling informed decisions in transformer design and manufacturing in accordance with IEC standards and Eco-design regulations.