yes you're rightv_c said:9V/30A --> 9V/400mA
Do you really need anything for this? If you have a source of 9V that
is capable of provining 30A, it will surely give you 400mA. On the other
hand the 9V source might not be regulated. Any converter that you put
will have a drop so your output will be less than 9V -- you might have to
go with a boost converter onthis one but your duty ratio may be very close to 0.
9V/30A --> 3.6V/350mA
9V/30A --> 5V/400mA
Again for these last two having the source be capable of giving you 30A does not mean that you will need to draw 30A.