Presidential Transition Enhancement Act of 2019 This bill makes changes intended to smooth the transfer of executive power during presidential transitions. The bill provides for the detailing of legislative branch employees on a reimbursable basis to office staffs designated by the President-elect or Vice President-elect with the consent of the supervising Member of Congress. The bill extends support provided by the General Services Administration (GSA) to the President- and Vice President-elect for up to 60 days after the inauguration. By September 1 of a year during which a presidential election occurs, the GSA shall enter into a memorandum of understanding (MOU) with each eligible candidate, which shall include the conditions for administrative support services and facilities. To the maximum extent practicable, an MOU shall be based on MOUs relating to previous presidential transitions. Each MOU shall include an agreement that the eligible candidate will implement and enforce an ethics plan to guide the conduct of the transition beginning on the date on which such candidate becomes President-elect. The plan shall be published on the GSA website. By September 15 of a year during which a presidential election occurs, each agency shall ensure that a succession plan is in place for each senior noncareer position in the agency.