When converting 120vac to 12vdc, does the wattage & amperage change?
In the ideal case it will draw 27W from the 120V too, but the conversion isn't ideal: you have heat losses in transformer, rectifier and voltage regulator, so your mains power will be higher. How much higher depends on the design quality of your power supply, but it can be easily 50% higher, so you could draw 40W.