Nowadays, it has become possible for universities and new businesses to launch satellites of reduced size and cost fulfilling viable missions. Nevertheless, there is still a considerable failure rate that reduces the expected lifetime of these spacecraft. One of the main causes of failure is the power system. Redundancy is one of the main options to enhance its lifetime and lower the failure rate. However, cost, mass, and complexity increase due to redundancy, making it more difficult to complete the projects. Thus, it is necessary to enhance the lifetime of power systems while keeping the development process simple and fast. This paper proposes two configurations of an electrical power system with duplicate components: single-bus configuration has been designed for a nanosatellite not yet launched and dual-bus configuration for a micro deep-space probe launched into a heliocentric orbit. The design and implementation of two dual electrical power systems are described; measurements and on-orbit data of the electrical power system of the micro deep-space probe are also presented, demonstrating that the dual-bus electrical power system can be successfully used in spacecraft. Lastly, conclusions regarding the redundancy considerations for small satellite electrical power systems are drawn based on these two examples.