Hello Bruce. S,
Everything obeys the raw of conversion of energy. Now matter how you conver votlage, total power remains unchanges.
If input source can only offer max 100w input power, it is impossible to get 113.4w output(54vx2.1a)
And from 12v to 54v, there is a large votlage difference. It may cause more energy loss, so actual output may not be as what you set.
Simple mode is regarding how to set output voltage/current, it is necessary operation.
Best regards.