I installed this in my RV:
2 USB outlets - one at 2.1A, the other at 1A.
If you will only be unplugged a short time, certainly the inverter works - but the losses converting 12vDC to 110vAC then back to 5vDC will drain the supply battery much quicker than just the 12vDC -5vDC adapter.
I do have an inverter with me if needed - but rarely use it...
Have a 12v adapter to power the laptop... and added a 12v TV in bedroom...
110 only needed for microwave and A/C - and those need the genny running.