When the North blockaded the South, they no longer could get as many war supplies as they needed, like powder. But they could also not get any of the other things they needed. Like medicine and certain food. That's one reason why so many men died in Andersonville. The south sent a delegation of released Andersonville prisoners to Lincoln to beg that medicine and food be sent to support his men in Andersonville with the promise that it was for his men only. But he didn't listen.
Regarding the North getting more benefits:
Senator Benton said in 1828 that the South "may be said to defray three-fourths of the annual expense of supporting the Federal government; and of this great sum, annually furnished by them, nothing or next to nothing is returned to them, in the shape of Government expenditures. That expenditure flows in an opposite direction--it flows northwardly, in one uniform, uninterrupted, and perennial stream."
George Lunt, author of Origins of the Late War, noted,
"In 1833 there as a surplus revenue of many millions in the public treasure which by an act of legislation unparalleled in the history of nations was distributed among the Northern States to be used for local public improvements."
President James Buchanan's message to Congress declared,
"The South has not had her share of money from the treasury, and unjust discrimination has been made against her."
In his January 1861 speech to the Georgia Secession Convention, Alexander Stephens said that 75% of the business done abroad, imports and exports, were done by Northerners. Government figures from the 1859-1860 period show that most import tariffs were paid in Northern ports by Northern consumers. In his speech Stephens also details how Southern postal deliveries were subsidized to the tune of over $6 million by the North. I think the claims that the South paid most of the taxes and received a disproportionately low amount of federal spending is just not supported by the facts.