300mAh instead of 1500mAh - damaging?

I have a battery charger that requires DC12V, but it's adapter is UK style, 
so I can't use it's original adapter.

The original adapter says it outputs at DC12V ~ 1500mAh.

Right now I'm using an universal adapter that outputs at DC12V, but ~
300mAh.

Would this damage the battery charger, or would it only charge slower?