Let's say I'm buying a portable power supply for my phone or laptop. I know my device can take a range of input voltages (for my mac: 5V, 9V, 15V, 20V, 28V; fo

Let's say I'm buying a portable power supply for my phone or laptop. I know my device can take a range of input voltages (for my mac: 5V, 9V, 15V, 20V, 28V; for my pixel: 5V, 9V) and know my device will negotiate with the power supply over USB-C for the correct voltage. Since my device can handle either, I would be equally happy with a power supply that used 5V internally as one that used 9V internally. So I do primarily care about the capacity of the power supply in Watt-Hours (energy).