Hi,
Thanks for the replies, I have been trying another smps, a black plastic block type from an external usb drive, and that does not give any interference.
The Arduino and the original internal smps are located 10 mtrs away and fed via a usb to RJ45 adapter pair.
If the cable, powered at the arduino end, is next to the display /pc there is no interference on the security cameras videos images, its only when plugged into the pc usb ports that the problem is evident. ( there is no interference obvious on the normal windows screen images)
RichD, wil try the resistor method you mention.