Electrical appliances sure are important in a shonen manga.
Enma probably has stored Haki from Oden, Enma right now is also eating Zoro's Haki and storing it, when the wielder of the blade is powerful enough to use it properly and release the stored Haki.... the damage becomes astonishing, that's what i think it is doing. AS LIKE I SAID IT ISN'T FULLY EXPLAINED YET AND EVERYTHING WE ARE TALKING IS JUST ASSUMPTION.