Usually, the bigger, more reputable brands have a pretty true power rating. Kicker are good, cause i bought a 600W RMS Amp and inside the packaging, they have a piece of paper saying that it was tested and so on, and passed everything, but that it was actually putting out 740W RMS instead.

yeah alpine does the same thing, got that little sheet with my amp saying meets 500rms but hit like max 580 or something, which is still in saftey limits