After finishing Optimize the powerplant, go speak with Gordon in Gecko junkyard. He will tell you that after the powerplant is optimized, Gecko can sell excess electricity to Vault City for medical services, and ask you to deliver some economy data to McClure in the Vault City in hope of making a business agreement.
Sometimes you cannot give the Economy Disk to McClure, effectively preventing the Gecko good ending. This has occurred on patch 1.02, and can be fixed by installing a patch.[verified]