With GPUs like the RX 470 the power consumption displayed there is only the GPU compute power and doesn’t include the memory controller power which is another 30-40 watts or so.
Another reason is the miner software has no idea how much power your motherboard, fan, SSD, cpus are consuming. These are usually 30-40 watts per system.
Another is your choice of PSU. You got a Good PSU with 90% efficiency it will use less power than a PSU with 75% efficiency.
Yes there is a difference. Different components inside the PSU determine how efficient it can be. The more efficient the more expensive parts it uses.
When a PSU says 400Watts, its the max power it can deliver to your computer. If the effiency is 90%, it means 10% is lost due to heat. So from the wall it might pull 440 Watts.
However the curve is most efficient when you are pulling around 50% load, so if you are maxing out the PSU, it might only be like 85% efficient and if you are only using 10% load it might also be 85% efficient. This is why there is usually a curve drawn on the box to show you this.