The upgrade of HVDC systems may lead to the addition of new converter stations or new interconnections, requiring the power reinforcement of certain existing conductors. To face this challenge, this work proposes to install a parallel conductor with the existing one (which would be the classical solution) and a power flow controller (PFC) connected between the two conductors to control their current distribution. The electric and thermal model of both solutions (parallel submarine cables with and without PFC) are presented. Then, the methodology to assess the economic interest of the solution is introduced, detailing the cost model and the workflow. The case study results show that for total transmitted powers of twice the initial power (power capability of the first cable) or higher, the solution with PFC becomes economically interesting since the reduction of cost of the second cable compensates the increment in operation cost due to power losses.