In the EE Times article "The 13-Step EMI Mitigation Program for Switching Power Supplies" CUI's VP of Marketing, Jeff Schnabel, examines 13 key steps that can help eliminate the issue of EMI.
The article begins, "The problems that EMI causes have been well documented and needs to be minimized at a system level. Ac/dc supplies and dc/dc converters are among the chief causes of EMI and the following looks at 13 key steps that can help eliminate this issue from your designs."
"1. Bypass capacitors connected directly between the power and return lines of the power supply will suppress differential mode conducted emissions. The power lines that require filtering may be those located at the input or the output of the power supply. The bypass capacitors on these lines need to be physically located adjacent to the terminals of the noise generating source to be most effective."