no familiarity with this game, but considering it's Sega, I'm going to lean towards it being one of the larger box type 200W power supplies. like one of the big XT types.
depending on if your power harnesses are already rigged to take a 9 pin molex off one of those stock, this could be an easy swap... and it might not. I had to splice my own connections on Daytona USA, so the typical colors Sega uses are different than the usual color standard. I forget what all exactly goes to the main board on those, been about 3 years since I did one, I'm thinking it's just +5 and ground, which are yellow and white respectively. I wanna say there was brown wires too, but in later hardware iterations that was for +3.3V, and did not exist on the System 1 and System 2's.