The DC Female Power Plug is used to terminate the power line side of Siamese cables to power security cameras. The Male adapter goes on the end that the camera is on and the female adapter goes on the end that the power transformer is on.
Both connectors have ⊕ and ⊖ next to each terminal, positive (red) goes in ⊕ and negative (black) goes in ⊖.
2.1mm DC Plug (Camera End)
Product Number: DC-Female-Power-2-Pin