Since there are 20 fewer mittens pairs than the plugs, there are 150+20 = 170 pairs of plugs.
When Gunner decides to add 30 more plugs pairs into the box of plugs, the number of plug pairs increases to 170+30 = <<170+30=200>>200
Since a pair has two, the 200 pairs of plugs total 200*2 = <<200*2=400>>400 plugs.
#### 400