The delivered price is the final price including transportation costs.
The definition of "delivered price" from Merriam-Webster is a price for which a seller agrees to deliver merchandise to a purchaser at a designated place and which usually includes the f.o.b. price at the shipping point plus lawful transportation charges actually incurred in delivery
Another few definitions:
From Cambridge Dictionary
Delivered price is a price for goods which includes the cost of packing, transport, etc.
From Financial Dictionary
Delivered pricing is the charging of a PRICE for a product that includes the cost of transporting the product from the manufacturer to the customer.
From Collins Dictionary
Delivered price is a quoted price of merchandise, as steel, that includes freight charges from the basing point to the point of delivery, usually f.o.b.
From Marketing Dictionary of Monash Business School
Delivered pricing is a pricing method in which the final price to the buyer is adjusted to include transportation costs; the seller takes responsibility for arranging delivery but adds the cost to the quoted price.
The meaning of the phrase is that the transmission (transportation) price of the electricity will not be affected, thus the final price including transportation - delivered price - will rise not so much.