Can I safely charge my Iphone 4s with a 1.5A charger?

I have a Sony portable charger, and on the manual it says that "Output 5V, 1.5A (Max)" and on my iPhone 4s adaptor it says that the output is 5V, 1A.

So, can I use the potable charger safely, or I need an extra adaptor?

What does that "max" mean?