Understanding portable music player's power specs
Those specifications are quite close. There are a few things to bear in mind though. They don't state what the levels of distortion are for the readings. If you imagine one using a pure sine-wave and basing their measurements on that and the other driving theirs into clipping slightly then the second will get more power but at worse distortion.

Now let's calculate power. If the amplifier can give out 8 V peak to peak then that's 4 V peak and, dividing by root 2 to get the true RMS, that works out as 2.83 Vrms. Now multiply this by 0.15 A and we get 0.424 W = 424 mW - pretty close to the specs. Chances are they're both using the same chip!

But, I hear you say, what about the 250 mA max current on the first unit? Well we don't know for sure. Note that they're not saying it will supply 250 mA at full voltage. I'd be inclined to believe the second unit's specs.

Mind your ears. :^)