The wind-driven triboelectric nanogenerator (W-TENG) is a promising candidate for energy harvesting because wind itself is a clean, ubiquitous and unexhausted energy source. A wind flow induces unpredictable chaotic outputs from the W-TENG, which are applicable to a random number generator (RNG) for cryptographic applications due to its inherent turbulent nature. Thus, the W-TENG with a two-in-one structure can simultaneously generate both power and true random numbers. The randomness of the generated random numbers from the W-TENG is improved by a structural change from a quadruple-clamped flip-flop membrane to a double-clamped flip-flop membrane. From a power generation point of view, the quadruple-clamped W-TENG is preferred. However, as far as randomness is concerned, the double-clamped W-TENG is more attractive. Thus, an end user can customize the amount of power generation and the quality of random numbers according to a target application. Here, we also evaluate the robustness of the randomness to environmental effects, such as humidity and temperature. By harvesting energy and producing true random numbers, the W-TENG can contribute to securing and self-powering a microsystem for IoT applications.