American Territories (Samoa, Palmyra, etc) can be downloaded for free in ENC or Raster ENC formats from
In fact the entire US is free. For all other countries you have to pay.
I recommend you do not use the NZ enc's. You can purchase electronic charts in many different formats. If you are using PC based navigation (like Fugawi) then I recommend "softcharts". It will run the free ENC's and a bunch of other formats. Otherwise you'll be forced to use the overpriced proprietary charting of whatever brand of chartplotter you have, Garmin being the worst for the South Pacific.