The Watt wars has been going on since the intro of solid state and went off the charts with the Japanese solid state invasion in the 80’s. Manufacturers have convinced just about everyone that if you have an 80 watt amp and a 100 watt amp the 100 watt amp is "better" and louder. In general the maximum watt rating of an amp is a worthless number for comparing amps within 2x (or more) the power rating. As someone mentioned dBs use a logarithmic scale so to increase the loudness by 3dBs (not much) you need double the power. So comparing that 80 and 100 watt amp there will be about a 1dB theoretical max increase at full power. You will never hear this!
More important is the design of the power supply and its power reserves. The watt rating is calculated with a constant tone played till it clips. But if a power supply has ample reserves it can deliver many times the wattage rating for short peaks without clipping. For most listening this is more desirable than having an amp with a marginal supply that barely covers its rating. To get a better idea about the real power output and how well it can drive a difficult load check the specs and see if it can double down (or come close) the watts going from a 8 ohm to a 4 ohm load. If it goes to 2 ohms even better. This gives a good approximation of how good the power supply is. I would take a 70 watt amp that doubles down over a 300 watt amp that only has a small increase in watts at a lower ohm load any day.
More important is the design of the power supply and its power reserves. The watt rating is calculated with a constant tone played till it clips. But if a power supply has ample reserves it can deliver many times the wattage rating for short peaks without clipping. For most listening this is more desirable than having an amp with a marginal supply that barely covers its rating. To get a better idea about the real power output and how well it can drive a difficult load check the specs and see if it can double down (or come close) the watts going from a 8 ohm to a 4 ohm load. If it goes to 2 ohms even better. This gives a good approximation of how good the power supply is. I would take a 70 watt amp that doubles down over a 300 watt amp that only has a small increase in watts at a lower ohm load any day.