Any 7- or 8-speed chain should work with your 7-speed cassette. I would not recommend using SRAM or KMC power link on a Shimano chain, but SRAM and KMC 8-speed chains on a 7-speed Shimano system should work fine.
Seeing as everything is fairly new, I'm suspecting the chain is too long. I'm a "long chain" advocate, so my method to measuring a chain is to break it so the chain doesn't rub on itself passing through the rear cage when shifted to the small-small cog combination. The head mechanic where I work is a "short chain" advocate, and his method is to shift to the large-large combination and break the chain so it makes an almost straight line through the rear derailleur. You might want to just split the difference.