Send it back or call Amazon and make them send you the correct P/S. Amazon has great customer service, so this should be a non-issue! A hassle, but not a problem.
And, if you are going to replace a P/S, the P/S is the MOST IMPORTANT PART OF THE AMP!!!!! Don't cheap out on it, buy the $40 supply and be done with it.
I will also mention, a regulated power supply is a poor choice for an amplifier P/S, and SMPS is an even worse choice. Un-regulated linear P/S is the technically superior choice.