An electrical power system may be provided with temporary power from a bank of supercapacitors connected to a bus of the power system. The supercapacitors may be charged from an output from a primary power source of the system during start-up of the power source. Output voltage of the primary power source may progressively increase and capacitor charging may occur at this progressively increasing voltage. Dedicated current-limiting devices are not required during charging. When temporary power is required the supercapacitors may be discharged sequentially in a series combination so that a high internal voltage of each capacitor is maintained and so that virtually all of the stored energy of the capacitor may be discharged to the bus at a usable voltage.