You didn't ask, but amperage depends on the load (the amplifier).* It's OK to use a power supply with a higher current rating.
But if the power supply is under-rated and can't supply the necessary current, the power supply voltage will drop and unpredictable "bad things" can happen... The power supply might go into protection mode and temporarily shut-down, a fuse inside the power supply might blow, or the power supply might burn-up and die.
The amplifier will "draw" maximum current when it's putting-out maximum wattage into the speakers.
...There is always voltage present at the power outlets in your home. With nothing plugged-in (or nothing turned on) no current flows. A hair dryer draws more current than a 100W light bulb but the voltage remains (about) the same. If you plug a hair dryer and a toaster into the same circuit, you'll draw excess current and blow the circuit breaker. (If a light dims when you turn-on the hair dryer, the voltage is dropping a bit.)
* Current is also proportional to voltage with a constant load. If you double the voltage into a speaker you also double the current, and that means 4 times with wattage. But with an active-variable load like an amplifier it's not as simple.