Dell Inspiron 15R not charging.

Hi. 

I have a Dell Inspiron 15R, which is a little over a year old.

I plugged it in to charge and the blue light on the adapter indicated that it is receiving power from the mains, but when plugged into the laptop, the laptop doesn't register that it is plugged in, also, when plugged in the blue light did dim slightly. I have borrowed another adapter, exactly the same as mine, and the laptop registers this one, and the light comes on to say it is charging. This suggests that I might need to buy a new adapter, but I would like advice on what to do. The adapter has been well looked after, it doesn't have any damage. 

Thank you in advanced,

~Kututo