AC outlet Modeling Mini Tutor.
Great, you've done well.I also cut the holes manually with the point-based snap on, focusing on the spline circles, which I did temporarily - I can see them at step 71. The first hole in the middle I applied [Chamfer] to the point, pushing it up to the circle. The second - which is great, is already a tool [Cut]. It is not necessary to do so since I, the main principle, and you have perfectly coped with it, the holes are ready for you.Now let's see why you had artifacts.You have "dangling" points left (I marked them red). Points should form quadrangles or in extreme cases pentagons (with this method of modeling). If this condition is met, then artifacts do not appear.You have "hanging" points form 2 large polygonal polygons - Fig.3 (highlighted in red). Such large polygons are inadmissible. When smoothing, the modifier tends to independently break this hefty polygon into quadrangles. There is a certain point to which everything comes down fig.1-2, at this point you get a bunch of edges that cause an artifact. To solve it, it's enough just for you to independently break these 2 polygons into quadrilaterals.Figure 4 shows an example from the lesson and a grid, cut by the [Cut] tool for one of the solutions to such problems.Figure 5 shows how you can do it yourself, adding ribs - are highlighted in green. The main task is to make quadrangles.You can make these cuts only on one quarter of the outlet (why "suffer" cutting the same across the entire model). After that remove the remaining 3 parts, and make the symmetry or mirroring of the first quarter, they are similar to each other.