He was, a Triple Rectifier to be exact. Also used a Marshall JCM 900 in the studio if I am not mistaken. Sometime after the "Self Titled" Blink-182 album he switched over to the AC30 and Twin Reverb at least for live performances (he had already switched to his signature Gibson ES333 by then).
And for what it is worth, "early on" as you put it, he was actually a Les Paul man. Still stripped it down to one bridge humbucker. From what I have read, all of the early Blink albums were recorded using a Les Paul and not his Signature Strat.