Danielleh, good question. I was thinking of picking up an additional power supply for the drive because I move it from the TV to PC and it's a hassle disconnecting it each time.
This is the spec: 12 Volts, 3 Amps, Mono Pin 5.5mm x 2.5mm, Polarity: Center Positive
from the Seagate site: https://www.seagate.com/support/kb/power-adapter-specifications-for-seagate-products/
A Google search came up this this: https://www.parts-express.com/12v-5a-dc-switching-power-supply-ac-adapter-with-25-x-55mm-plug--120-056