He doesn't know what he's talking about. They all use the exact same output chips. The differences between the C and JW version is almost certainly minor, again mostly with the power supply. Swapping parts between these 2 models will almost certainly be fine. As far as ratings go, if we take some whiteout and change the numbers in the back so that they look better, will that make one sound better than the other? The numbers are not set in stone -- they are subject to interpretation and depends entirely on how they are rated. In other words, maybe one rates it with the power supply installed in the boombox and another rates it on the bench using entirely different set of consumption parameters. The ratings will be different but both will be accurate. Also, how about if a PS with exact same components is rated at 61w at a 50% safety margin but the 70w one is rated at a 35% safety margin? Does the 70w one become more powerful as a result?
As for a power supply affecting the output capability of the boombox itself, it's plausible IF and only IF the boombox is drawing enough current to cause a droop in the supply voltage currently installed in which case, a stiffer supply that can maintain the power level will enable the boombox to perform better. Then again, if you are referring to power supply as the transformer, check them out and you'll note that they are probably identically sized. It's fair to say that a higher VA rated transformer will almost certainly be larger, as the ability of the transformer to output current depends upon the gauge of the windings and the number of turns to determine the voltage split. Thicker gauge windings take more room, so the transformer will be larger. So as long as the power supply is outputting the same voltage to the amp board (regardless of input voltage), then for all practical purposes, the boombox should roughly output the same. Anyhow, this has been discussed before, many times before already and various suffixed versions (of JVC) vs. power output is really nothing to even argue about. It's like asking how many more mm taller are you than I? Maybe it depends on what shoes you are wearing?
Bottom line, IF the power supplies are working the way they are designed, in the region they were released, then the output voltage sent to the boombox should be roughly the same and therefore, similar performance should be observed. It is after all, the voltage that the boombox sees that is important and controls how much power output it produces. Current consumed by an amplifier is supplied by the transformer based on demand (and same voltage means same current consumption) therefore, except for operating conditions where the boombox is at or near maximum volume where a voltage droop would manifest, wouldn't even be noticed. However, at maximum volume, if one power supply is stiffer, then that boombox will likely perform better.
Now, that being said, it is not uncommon for folks to use japanese domestic imported models (in this case, Victor M90) connected directly to North American voltage. Because transformers convert voltages in a set ratio, the victor model will output approximately 20% more voltage when connected to north american mains. This instantly makes the boombox feel more powerful but could risk damage to the device, especially with long term use. If you've ever ran a japanese model on USA power, you'll know what I mean... the VU's will swing higher, the boombox will feel more powerful overall, but at maximum volume, you may observe significantly greater distortion and of course the VU's will no longer be properly calibrated. This effect varies by model and manufacturer since it all depends upon how much internal regulation was designed into the boombox. The amplifier portion is typically fed unregulated power. How the rest of the boombox gets their power varies. Tuner and digital circuits typically have very precise voltage requirements and would be fed through voltage regulators (which would become stressed since they have to sink more thermal energy). Preamp and other circuits are sometimes regulated, sometimes not. I would not operate a Perdisco model on USA power without first swapping out the transformer. However, the Panasonic RX-7200 is practically a world beater with the 20% higher voltage supplied with the original japanese transformer. Just my observations.