Does a step-up power converter cause move volts but less amps?
Your options:


An inverter that converts 5v DC to 110v AC. But they don't exist.
Convert 5v to 20v, but you would need to have a very well regulated step-up converter, otherwise you'll kill your laptop. Also, you may have trouble finding one that is capable of outputting over 3 amps.
Step-up converter from 5v to 12v, then use a 12v DC to 110v AC inverter. But you may have trouble finding a 5v-12v inverter that can supply enough power (watts) or current (amps)


The way to calculate amps and volts, is by this simple formula:

P = I V

or in English, Power = Current (amps) x Volts

So if you have a car battery, say, 12 volts, and you want to power a laptop, 110v, 1 amp, you can calculate the power of the laptop, and from that, work out the minimum current that would be drawn from the 12v battery:

Laptop power = 110 x 1 = 110 watts.

Substitute that into the same formula for the battery:
P = I V
110 = I x 12
Therefore I = 110 / 12

So the car battery would need to supply 9.1666 amps to the inverter to power the laptop.

But there would be inefficiencies - the inverter would be at least 10% inefficient. And the same goes for the laptop power supply.

So to answer your question, yes - if a step-up converter doubles the voltage, then it can only output half the amps. (Or consume twice as many amps. Same thing)