Hello kinda my first post I really need some help with repairing these super nintendos i bought from craigslist for 15 bucks! I got 2 original and 2 mini's

they all seem to need the power jacks, After watching countless videos I really don't want to go to the hyperkin replacement route and would like to know it someone could point me in the right direction on how to do.. 

that power input jack mod thats on that snes and also one of the snes' was covered with corrosion after attempting to clean it up I noticed

the blue cap is missing on one of them any ideas how to replace it? yup thats the one with the massive amounts of corrosion on it