@DogsGalore,

We currently do not sell power supplies separately, and this is something that is only done when a defect is found. 

I think a large portion of this reasoning is due to the large variation between power consumption, even amongst the same model with a different length.

This is a request that we see often, so I will see what I can do about recommending we add them as an accessory - or at least providing some detailed instructions to help ensure you are purchasing a compatible power supply.