Owing to the increasing power density of a switching power supply (SPS), the placement of the components for thermal management and electromagnetic interference (EMI) characteristics is more difficult to design at a given form factor. When thermal management is a critical issue for the SPS, then methods for improving EMI noises seem not to be simultaneously successful at this design stage. As a result, the conducted EMI noises will deteriorate due to the placement of components for thermal management. Furthermore, the performance of the designed EMI filter will deteriorate due to severe internal electromagnetic interference, and thus lead to failure in the EMI conducted measurement. To improve this condition, the locations of EMI noise sources, modes of conducted EMI noise, their coupling paths and the characteristics of the electromagnetic field are investigated in detail. Various shielding schemes are proposed to reduce the EMI inside the SPS. Through this, the interference between the EMI sources, coupling paths and receivers can be significantly reduced so that the conducted EMI measurement of the SPS can meet the requirements. Finally, the effectiveness of the shielding schemes is demonstrated by some experimental results and some EMI reduction methods are suggested.