The amps should work fine as long as you keep their current draw below the 3A that the power supplies can provide - i.e. keep their output well below maximum (bear in mind that the amp will draw significantly more power than it delivers to the speakers).
If you exceed the rating of the power supply, the voltage will begin to sag and/or become unstable and you'll get audible distortion. Depending on the precise design of the amps and power supplies, one or both of them may shut down on detecting "abnormal" power supply conditions. The power supplies may also be damaged by being overloaded.
If the power supplies are of low quality with inadequate safety features, there is a chance they may catch fire. If they are this poorly designed, though, all bets are off as to what happens to their output voltage when things go badly wrong - they may present mains line voltage to the amp, which would probably destroy it.