Amps - Same at 12 volts as 120 volts?

If I have my computer running on a 120 volt power inverter connected to a 12 volt power supply, how do I calculate the draw on the 12 volt system based on a 12 volt current?

Do the amps stay the same? Do the watts stay the same? Do they both change...?

Readings from a "normal" in house outlet: 120.5 volts / 3.90 amps / 311 watts

12 volts / ? / ?

I assume the amps are * 10 so 3.90 would become 39.0 amps (12 volts / 39.0 amps / 311 watts?)

Or would this all change based on the type of inverter I use?

Any help would be much appreciated.

Best regards,

Dr34m3r