EU power adapter for UK laptop
Probably overkill, but that is irrelevant. The rating of the cable need only be the same or higher than the rating of the original. It may be worth changing the fuse in the plug (if it has one) to a 3A fuse to match the original cable, but the fuses in the plugs are typically there to protect the cable from melting, not the device connected to it, so changing it is not essential.

The leads are purely passive - that is to say they contain no active parts. In fact it is simply 3 copper cables and some insulation. If the cable has a higher rating, it simply means that the copper cables are thicker, not that it will deliver more current.

The only disadvantage of using the higher rated cable is that it will be physically larger - less flexible, harder to pack up into a neat space for travelling.