Sorry, but I think you’re splitting hairs with the amps. For practical considerations, one is not any more powerful than the other.
I know it is silly to be concerned with such a difference, but I really want to invest my money on the best possible piece of equipment, one that could be useful to me, and that I could enjoy, and even be proud of, for decades to come. This, along with my natural curiosity, makes for a hell of a treasure hunt.
At the Onkyo’s retail price of $499, Yamaha’s contender is the A-S501, not the 301.
It seemed to me that, as fas as power is concerned, the A-S301 would be the most fair contender. If we compare the Onkyo A-9150 to the A-S501, then the power difference is even bigger, but for the price it seems a very nice amp.
The A-S501 has the stronger power supply
By the way, I think the transformer of the A-S301 is rated for 6A, and the A-S501’s is rated for 8A. I couldn’t find anything on the Onkyo A-9150, but it is really similar to the 301’s. As for topology and regulation and other more technical stuff, they also seem similar to me, but I am no expert.