The difference between energy and power can take some time to wrap your head around. The mAh rating for the cells is also a bit misleading. mAh stands for milli-Amp Hours, which is thousandths of an Amp over an hour of time. The figure basically means that the amount of power stored in the cell, if discharged from full to empty in one hour at a linear rate, would be equal to 3.5 Amps of current flow. We use this mAh figure in place of the Amps part of the Wattage equation when working with batteries due to stored energy working a bit differently to linear energy supplied by a wall socket. In the case of a wall supply, you would just use the Amps figure listed on the supply to calculate the Wattage if the Wattage is for some reason not listed.

Also, the maximum discharge rating of the cell (which in this case is listed as 8 Amps) is an entirely separate figure to the cell's capacity, being a measure of true Amperage output rather than the time relative mAh figure. The discharge rating is what you use to ensure that the cells are able to put out enough current to run the system, which isn't so important for the PS2 or Wii due to their very low power requirements. This discharge rating is sometimes listed as C, which is how many times in one hour the cell can discharge its entire capacity. So a figure of 5C on a 3500 mAh cell would mean you multiply 3.5Ah by 5C to get 17.5 Amps as your max discharge figure. It's not really relevant to this use case, but the more you know.

Also also, it's worth remembering that wall supplies for consoles are specced to overkill to handle spikes in power consumption. The console doesn't use the maximum Amperage of the stock power supply at all times, so it's good to check (as you did) if anyone has measured the actual power consumption of the system so that you can source the correct parts.