Why is CL1 always below the advertised standard e.g. 80GOLD.
CL1 and CL2 are theoretical tests, neither will ever be realized in reality. If you take a look at the spec sheet for that PSU you'll see that it has a combined 3.3 and 5 volt power limit of 140 watts.
Since power (P) is simply current (I) times the node voltage difference (V, voltage, like height, is always relative between two points) we can see that the 3.3 volt rail can handle 25 amps or a maximum of 82.5 watts and the 5 volt rail can handle 25 amps or a maximum of 125 watts. Together these cannot exceed 140 watts without exceeding the PSUs design parameters. JonnyGURU decided to max out this test by drawing a little over 16 amps on each of the 3.3 volt and 5 volt rails which is very close to 140 watts.
In the early 2000s Intel realized that 5 volt main power was inefficient and would pose problems for the high-power Pentium 4 CPUs. Intel revised the ATX specification to put much more emphasis on the 12 volt supply and revised their power delivery mechanisms to follow suit. The rest of the PC industry soon followed. The result is that the 3.3 volt and 5 volt rails are hardly ever used, while almost all the load is on the 12 volt rail. Some compact platforms use only 12 volt supplies, omiting 3.3 volt and 5 volt supplies entirely.
So, 79.9% efficiency on rails that don't even matter much at all is still very impressive considering that most of their pre millennial counterparts were in the 60-75% range.
The real awesome part is 87.7% efficiency at nearly 100% load on the 12 volt rail which supplies more than 10 times the peak power as the 3.3 volt and 5 volt rails.