My lead doesn't work with my plug

Hi,

I have the original lead that came with my iphone 5. And the original plug, they have always worked fine but 2 nights ago I realised my phone wasn't charging when it was turned on but charged fine when it was turned off.

I then was tried my plug with a different lead and it worked fine, so I then tried a lead with a different plug and it worked fine but for some reason they just don't want to work together anymore...

Any ideas?

Thanks