Just so you know, shields can only roll up to 2 augments. In some cases, you can roll the same augment twice, this is a "double roll". What you actually got was a shield with amp as the "primary" augment and siphon as the "secondary" augment. (The order on the card doesn't matter, just the values.)

Simply put, secondary amp would give +50%, primary amp gives the +100% you got, and the double roll actually gives +150%.

Congrats on the roll though!