Supercontinuum generation using photonic crystal fibers is a useful technique to generate light spanning a broad wavelength range, using femtosecond laser pulses. For some applications, one may desire higher power density at specific wavelengths. Increasing the pump power results primarily in further broadening of the output spectrum and is not particularly useful for this purpose. In this paper we demonstrate that by applying a periodic spectral phase modulation to the input pulse using a pulse shaper, the spectral energy density of the output supercontinuum can be enhanced by nearly an order of magnitude at specific wavelengths, which are tunable.