Wierd things can happen with wall outlets and home AC power systems in general. I depends on how the system is wired.
I see what the concern is here.
First of all is the issue of amp power ratings. Typically amplifiers are rated by running a sine wave through the amp to a resistive load and then noting at what power output 1% or 10% THD is measured. Important to note that this is done with a SINE wave. Sine waves are very different from music: they are continuous, have no harmonics, and have a different crest factor. Crest factor is important here. Crest factor is basically the signal difference between peak and RMS. For sine waves this is ALWAYS 3dB. For music it varies. For pop stuff, it could be 6dB, for more dynamic stuff it could be as high as 20dB.
Now,
The point of a well designed power supply should be to account for everything: low and high line voltage (usually designed to account for +/-10%), rated power out of the amplifier, temperature, etc.
So,
If the amplifier is designed well, it should draw all it's instantaneous peaks from the power supply, and NOT from the line.
Typically, with an unregulated power supply in an amplifier, the droopage of the voltage rails in the box will be related to the power transformer more than anything. When magnetic flux of the core starts to saturate, the voltage will droop. This is why really nice amps sometimes have HUGE toroids in them.
Bottom line is that for a TYPICAL LINEAR AMP a 200W SS amp will NEVER be dumping 200W continuous into speakers. Think about it in the terms described above. If the amp is rated at 200W, that means that it can pass a sine wave to a specified load at 200W. For the sake of arguement, lets say the amp is mono, is a voltage amplifier, and the power supply is linear, and that the load is 4ohms. So that means that the load is seeing 28.3Vrms. If the amp trys to deliver more power to the load, it will square off the wave and sound terrible. This is the ceiling on the performance. Therefore, with music with a crest factor of 20dB, and running music signal in with no sqared off peaks, the RMS level of music would be around 2.83Vrms at the load with peaks as high as 28.3V. This translates to about 2W or average music signal. Now this is very controversial in the industry, but it's a much better way to understand this stuff than with just sine waves.
This explaination doesn't cover transients really. So what's the worst transient really? a 20Hz pulse at full peak (28.3V). The power supply should store enough juice to be able to deliver this to the amplifier. What would happen is the resivoir capacitors in the power supply would drain to provide the current necessary to drive the load. Then it would start to charge back up after the transient (MUCH slower than the speed at which the transient hit). Now you may ask, what if it's hit repeatedly with 20Hz transient peaks. Well, the answer is that that is very very very unlikely in music, and any well designed amp should account for all these things.
Now, all this discussion focuses on standard, voltage amplified, linear supply, solid state amps. There's a lot of wierd stuff out there that might act differently.
hope this helps..
You could always take a reasonably equipment multimeter and measure some of this stuff for yourself.