100V AC 50/60Hz 150W.
You will find this at the back of many japanese amps, notice also, that there are convinience outlets at the back of the amp, sometimes, they will be labled as "switched" and/or sometimes, "unswitched", ever noticed them? Some amps can have as many as three of those.
So now, what the power ratings means is that you can only plug in other appliances at the back of the amp not exceeding the power of 150 watts, so at 150 and 100volts, this is 1.5 amperes, not much i would say.
Now, for the power rating of the amps inside the box, we have to look at the rails used, look at the filter caps and it will give you a clue, most listening is done at 2 to 5 watt levels anyway, so this is still plenty.