For electronic thermal management with hydrated salt phase change materials (PCM), supercooling and thermal stability usually inhibit its development. In view of this, novel of disodium hydrogen phosphate dodecahydrate (DSP)-based composites PCM with miniaturized size is developed to solve these problems. Three kinds of carbon fillers employed as both nucleating agent and heat transfer promoter were added in DSP separately. The influences of carbon fillers' specific surface area, particle size, and adsorption mode on thermal properties of DSP-based composites PCM were investigated experimentally. The thermal conductive chains of composites PCM were detected by energy dispersive spectroscopy. The supercooling degree was analyzed by melting-freezing test. Temperature-regulated property was captured by infrared imager. In the present work, the supercooling degree of GNS/DSP composites PCM is efficiently reduced to 97.24% compared with the pure DSP. Negligible change in phase change temperature of the CNTS/DSP composites PCM was confirmed after 200 times cycles. There was no obvious liquid leakage of DSP when 2 wt% of carbon fillers were added in composites PCM. The enhancement on thermal properties of DSP is a promising strategy for numerous thermal applications.