Replacement power cable for Mindstorms RCX I have an old Mindstorms 1.5 RCX. 

The plastic on the power cables has degraded, and they short out and don't work well.

These look like they would work as replacements, but I'm not exactly sure. I contacted the seller but they didn't respond.

Will these work as replacement RCX power cables?
The cables you point out are newer Power Function cables and are ill-suited for 9V usage such as with the original Mindstorms kits. Technically, you could daisy-chain two of them and it would work, but that's probably not the best solution.

Here is a bigger illustration of the cable, courtesy Philo:



You can clearly see that only one end of the cable has a 9V connector on the bottom.

I would advise you to check Bricklink instead, you should find plenty of seller there, possibly in your own country.