Del. Code tit. 26, § 207

The Commission, by or through its members or duly authorized representatives, shall at all times have access to and the right to inspect and examine any and all books, accounts, records, memoranda, property, plant, facilities and equipment of public utilities. Every public utility shall furnish to the Commission, within such reasonable time as the Commission may order, any information with respect to its books, accounts, records, memoranda, property, plant, facilities, equipment, service, and operations, which the Commission may require in aid of any inspection, examination, inquiry, investigation, or hearing, or in aid of any determination of the value of its property, or any portion thereof, including copies of accounts, records, books, maps, inventories, appraisals, valuations, contracts, reports of engineers, and other data, records and papers; and shall grant to all authorized agents of the Commission access to its premises, property, plant, facilities and equipment and its books, accounts, records and memoranda when requested to.