In recent years, the electrification and automation of vehicles have achieved significant progress. Highly ensured 12V power supply is a prerequisite for electric vehicles with driving automation, particularly for some safety-critical functions, such as vehicle computers. A so-called high-available 12V power supply can guarantee a safe and uninterrupted 12V power supply for vehicles. To achieve this objective, one possible approach is to use redundant power sources, e.g. batteries. Alternatively, a DC/DC converter with high availability can be used, which is defined in this paper as a high-available DC/DC converter. This paper introduces the definition of high availability as well as high-available DC/DC converters and presents three promising different variants of high-available 12V power supply systems for automated electric vehicles. Furthermore, a pragmatic and generally usable procedure is proposed to compare the presented different variants of high-available 12V power supply systems by using relevant quantitative as well as qualitative criteria. Finally, an exemplary comparison of three different variants is presented, from which the most promising 12V power supply system with high availability is selected for future automated electric vehicles.