An offshore oil and gas platform has a power supply system with a cascaded arrangement for a black start. The power supply system includes a first power supply apparatus for providing power at a first energy level, an uninterruptible power supply arrangement configured to receive power from the first power supply apparatus, wherein the uninterruptible power supply is for powering at least one essential and/or safety critical component, and a second power supply apparatus for providing power at a second energy level to a main power distribution system, wherein the second energy level is higher than the first energy level, wherein the second power supply apparatus includes a power source and a high-power energy storage system capable of supplying power at the second energy level, and wherein the second power supply apparatus can receive and store energy from the first power supply apparatus.