question about installation of 20 amp wall plug

I bought a replacement wall plug that is rated 20 amps. I installed it from a 15 amp circuit breaker, in the add it said it was ok to use in 15 or 20 amp. I pluged in a cheap intergraded amp to it and it and my speakers started popping and the amp started to smoke, I unplugged it right away. Was I wrong to assume that it would be ok coming from a 15 amp circuit, can anyone tell me what I did wrong, thanks