Power transformer (PT) is one of the most important parts in electrical power system. In some cases, many electric utilities do not consider to capitalize the power losses, resulting in uneconomical decision during the purchasing. In this study, to evaluate the best purchase choice of a 60 MVA 150/129 kV PT, we examine the total cost of ownership (TCO) as the basis for determining the total economic value of PT. When purchasing and designing the PT, the optimum parameters are not only solely determined by the design and the lowest cost, but also influenced by material cost, power losses and its typical operation. Hence, design optimization and calculation of TCO of PT is of importance to provide a reliable and economical product. Here it is realized by reviewing the existing design and fabrication as well as the cost structure, design optimization and total cost ownership calculation. The result shows that the PT design optimization employing losses capitalization exhibits the most economical value, reducing TCO up to 3%. We found that the losses capitalization and TCO of PT are sensitively affected by interest rate, economic life of PT, electricity cost, load factor and losses. Those factors are key components to determine the suitable specification, design evaluation and operation of the transformer. This practical study is beneficial both for the owner and manufacturer of PT, thus giving the right specification and design to support purchasing process of PT.