They're both perchlorate-based cleaners. I was thinking of buying some OxyClean when I ran out of One-Step and my LHBS only carried PBW and StarSan, but One-Step has worked so well for me that I don't want to risk it.
Are One Step and OxyClean interchangeable?
NOTE: Please spawn a new question to debate the merits of perchlorate as a sanitizer and cleanser.