Power generation of an Imperial Star Destroyer.
I will use a low-end power generation for an Imperial Star Destroyer. The Death Star has a diameter of 160 Kilometers, which is roughly the size of the Moon Puck. The Moon Puck has a mass of 2.9e+18 Kilograms. Since the Death Star has corridors I will divide the mass by half, so the DS's mass is 1.45e+18 Kilograms. An Imperial Star Destroyer is 10 million times smaller than the Death Star, so it would have a mass of 145,000,000,000 Kilograms, or 145 million metric tons. In Attack of the Clones we see Imperial Star destroyers leave Coruscant's gravitational pull. Since Coruscant's population is humans, it's safe to assume that Coruscant has gravity like Earth's. To escape the Graviational pull of the planet you need to be at least mach 33, which is 33 times the speed of sound. The energy requirements just to send one Kilogram to that speed and sent it to space is 63 Megajoules, and to maintain said speeds it will need to continuously expend that much energy. So the Imperial Star Destroyer would have to expend 9.142E+18 joules every second to achieve escape velocity speeds, which means that they're expending 2,185 Megatons worth of energy to achieve those speeds. In comparison the most powerful Nuclear Bomb ever built was only 50 Megatons. They can easily use that energy into their weapons because even the Death Star only uses 1 reactor to generate all their power to all of their systems, even the Superlaser. So the Imperial Star destroyer, which is less advanced would also only use 1 reactor. I also argue that the fuel they must be using is at least converting mass to energy, since the amount of fuel they would have using fusion would have reactors bigger than their ship, while converting roughly 100 Kilograms to fuel generates roughly the amount of energy they need to expend to reach escape velocity speeds.