The power amp rating is telling you that it requires no more than 30mA. The converter rating is telling you that it can deliver anything required up to a maximum of 300mA.
As long as the converter rating is greater than the demands of the power amp (as you describe) then it will be fine.
Be sure to observe proper polarity or you may get smoke.
As long as the converter rating is greater than the demands of the power amp (as you describe) then it will be fine.
Be sure to observe proper polarity or you may get smoke.