The 112MW figure is the estimated shp delivered by the 4 GT in 2x COGAG config. Electrical power is provided by 6 GT power generator sets providing anywhere from 18MW (lower estimate) to 48MW (upper estimate) of electrical power.
The Zumwalt has a lot more flexibility with its power distribution than the 055, as its propulsion is electric driven.
That might be true for the current iteration of 055s which don't yet have IEP but it won't be true for the followup sub-class, 055A. Four QC280s will provide the IEP vessel with ~100MW of power, plenty to play with.
From the picture below, the ship beside the 072 LST seems laden with electric equipment and electrical panels. Curious that they are heat generating and why are they painted black in addition to being in the hot sun.
But the point I want to make is that if the LST plus additional containerised generators are enough to power the rail/coilgun, why is the ship beside it carrying so much electrical equipment? The ship beside it seems to be a support ship. Why does a support ship need so much electrical equipment? A support ship for a complex rail/coilgun would probably need to have data servers and advanced electrical diagnostics equipment (oscilloscopes etc.). But those aren't necessarily voluminous as to need to be distributed throughout the ship next to the LST. There are full 2metre height standing panels (beige coloured with their own roof) even on the 'roof' of that ship as well.
That's a construction barge used to assist with setting up and maintaining the construction site. There's one parked next to the 055 right now to assist with its construction. They are not related to the design of the ship under construction/modification.
The railgun system is compact enough to be hosted by a 072.