The standard power cable for computer works just fine, available almost anywhere and is less expensive then buying through HI equipment suppliers. Length hasn't affected any of my findings. I've tested different lengths on the same circuit just to make sure
If and when yours malfunctions in the field you always have a back-up as long as your computer battery is charged and will last for the rest of your inspection.
Also take your tester with you and try different cords. I've found the pin tension seems to vary and "tighter is better"
