The cooling of electronic gadgets is the biggest challenge in recent years. The selection of innovative cooling techniques leads to the improvement in reliability and performance of electronic systems. Hence, the present study deals with the 3-D numerical modeling and simulation of seven high power protruding heat sources mounted on an SMPS (Switch Mode Power Supply) board using ANSYS FLUENT (R-16) under transient heat transfer mode. The heat sources are cooled under air medium using a velocity of 15 m/s and the heat dissipation rate is 10 W/cm2. The objective is to study the surface radiation effect on the cooling of these heat sources under forced convection and to analyze the heating and cooling cycle of the heat sources. Four different surface conditions (ϵ = 0.90, Non-metallic paint), (ϵ = 0.86, Gray surface, ϵ = 0.8, Steel oxidised paint) and (ϵ = 0.65, Fe-Cast surface) are considered to analyze the radiation effect and the values are compared with respect to the polished surface (ϵ = 0.1). It has been concluded that the surface radiation reduces the temperature of the heat sources by 18 to 25% and helps in better cooling. The time taken for both charging (heating) and discharging (cooling) of the heat sources are also reported for the above emissivity values, and it has been found that charging (heating) takes more time as compare to discharging (cooling) of the heat sources. To generalize the problem, a correlation is put forward for the non-dimensional temperature excess (θ) of the heat sources in terms of their surface emissivity (ϵ) and cooling rate (time). © 2020 Author(s).