This question is rather complicated since your laptop's power consumption fluctuates a lot depending on if you're gaming or simply browsing the Internet on the laptop. This affects the time and percentage Omnicharge can charge your laptop.
So to simplify the question, we use a more objective method by comparing Omnicharge's battery capacity to the laptop's internal battery capacity. Also considering the efficiency loss of Omnicharge's conversion circuits, the equation of charge percentage is:
Omnicharge's battery capacity / laptop's internal battery capacity * Omnicharge's conversion circuits efficiency
Take the Omni Mobile 25,600 and the 15'' MacBook Pro (2019 model), the Mobile 25,600 has a 92Wh capacity and the 15'' MBP has an 83.6Wh internal battery; the Omnicharges conversion efficiency is around 90%. Put these numbers in the above equation and we get:
92Wh / 83.6Wh * 90% = 0.99
This means that the Omnicharge can charge the 15'' MBP around 1 time, effectively doubling your laptop battery life. This is assuming that the laptop is turned off or in sleep mode. Operating the laptop while charging will impact this calculation. The equation will be the same for both the DC output and the USB-C output, as these have very similar conversion efficiencies.
Remember that you might get significantly different results in real life. Let's say that your laptop battery is already fully charged, and you are only using the Omnicharge to extend the battery life. Since the laptop battery is already full, the power draw will be significantly lower, which also means that the Omnicharge will output less heat, and will, therefore, have higher efficiency.