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 both Omnicharge's conversion circuits and the laptop's power adaptor, the equation of charge percentage is:
Omnicharge's battery capacity / laptop's internal battery capacity * Omnicharge's conversion circuits efficiency * laptop's power supply efficiency
Take the Omni 13+ and 13'' MacBook Pro (2019 model) for example, the Omni 13+ has a 47Wh battery; the 13" MBP has a 58 Wh internal battery; both the Omnicharges conversion efficiency and the 13" MBP's power supply efficiency is around 90%. Put these numbers in the above equation and we get:
47Wh / 58Wh * 90% * 90% = 0.65
This means that the Omnicharge can charge the 13'' MBP around 65%. This is assuming that the laptop is turned off or in sleep mode. Operating the laptop while charging will impact this calculation.
One of the advantages of the USB-C output is that you don't need to suffer from the laptop power supply's efficiency loss. And the above equation becomes:
Omnicharge's battery capacity / laptop's internal battery capacity * Omnicharge's conversion circuits efficiency
Again take the Omni 13+ and 13'' MacBook Pro for example:
47Wh / 58Wh * 90% = 0.73
This means that the Omnicharge can charge up 13'' MBP for around 73%. That's 8% more compared to charging from the AC outlet.