A fuel supply system for a gas turbine engine has a fuel tank, a main fuel pump for receiving fuel from the fuel tank, and an electric pump also for receiving fuel from the fuel tank. The main fuel pump and the electric pump both deliver fuel to a sharing valve. The sharing valve selectively delivers fuel downstream into a gas generator portion of the gas turbine engine and to an augmentor. A control is programmed to control the sharing valve, such that fuel flows from the main fuel pump to the augmentor, and to the gas generator at higher demand operation, and does not flow from the main fuel pump at lower demand operation. A gas turbine engine and a method are also disclosed.