They usually leave a good margin on the original PSUs in my experience,
you should be fine with a 300.

How long does it last on a set ofgood XmAh rechargables? From that you
can work out roughly the actual current draw and decide for yourself.
Generally though, IMO, you can draw a little more than the PSU states
without worry, and they supply a PSU with items that can handle a fair
amount more than the item draws.

J