A mortgage or bill of sale to secure debt may embrace all property in possession, or to which the mortgagor or grantor has the right of possession at the time. A mortgage or bill of sale to secure debt given by a person or a corporation to a trustee or trustees to secure an issue of bonds shall, when it is expressly so stipulated therein, embrace, cover, and convey title to after-acquired property of such person or corporation. Provided, however, any public utility company, whether or not incorporated, including, without limitation, any corporation organized under or governed by the provisions of Article 4 of Chapter 3 of Title 46, may by mortgage, bill of sale to secure debt, deed to secure debt, or deed of trust, embrace, cover, convey, pledge, and encumber after-acquired property of such company, wherever located, when the instrument expressly so stipulates therein; and any such instrument when recorded as provided by law shall constitute notice from the time it is filed for record and shall have priority (subject to purchase money encumbrances) as against the interests of third parties with respect to after-acquired property from the time such property is acquired.