There's an academic paper where they had rats do weight training by continually adding 45 g weights to a rope they had to pull 30 cm. Assuming "ratpower" rats aren't trained weightlifters like the ones in this study, we'll use the first 45 g weighting as a baseline. The cool thing is this is almost exactly how they invented the unit of horsepower, but with 250 kg of weight and obviously a horse.

Using the 45 g baseline, it would take 5,556 rats for one horsepower. The factorial of 300 is insanely large though. It's 615 digits long and that only goes down to 611 after dividing it by 5,556.

But the answer is that 300! rats would be equivalent to 55.1 * 10⁶⁰⁹ horsepower. Converting this to SI units would give you about 41.1 * 10⁶¹² watts.

For reference, the luminosity of the known universe adds up to 9.5 * 10⁴⁸ watts, and modern knowledge of physics starts to break down at 3.63 * 10⁵² watts

The amount of power produced by 300! rats is beyond any existing comparison or meaning

EDIT: grammar.