I'm putting this down as your laptop is power throttling the components.
The thing with a lot of modern gaming laptops, especially cheaper or thinner ones, is they tend to be thermally constrained either because the manufacturer cheaped out or it physically cannot support it. So they can only dissipate so much power safely. They try to market this as the GPU or CPU can use less power so the other can use more, but you're never going to get both of them running at full power at the same time. For reference, AMD markets the 5800H as having a TDP of up to 35-45W, while Acer says the GPU you have is the 90W version.
Also consider what else needs to run on the computer: the main board, the other components, and the display. That adds about another 20-30W. So we're up to about say 125W. Then you need to factor in the power required to charge the battery when it's low as this is period where the battery can accept the most current. So let's call this at 30W. Then you want to have enough overhead in the power brick so you're not going to be in a state where it's 100% for extended periods of time. So putting this altogether, 155W extended power use on a 180W power brick seems reasonable.