Interval branch and bound is a computational algorithm for global optimization, and was applied to the design of AC-DC flyback converters. This paper discusses the algorithm and the specifics of its application to flyback power converter design, including the choices of objectives and optimization variables. It includes discussion of specific designs, and presents statistics of the algorithm performance for a range of specifications. Finally, the interval branch and bound performance is compared to design optimization by exhaustive search and found to be superior in computational time. The results of this work are validated on a USB-PD power adapter application.