I just got a Powerline adaptor that supports Gigabit Ethernet and 1200Mbps, since my WiFI connection was inconsistent (despite being quite strong). For some reason, it delivers MUCH slower speeds than my WiFi connection. My WiFi here delivers a steady 270Mbps, while the Powerline delivers around 45~50 Mpbs (have up to 1000Mbps from my ISP, and this is with a 5G ac WiFi). I would hope I would get 500Mbps, as I get from Ethernet cables connected directly to the router. Both adapters are connected directly to power with no strips or anything. I'm pretty sure they are on the same circuit (they are on other sides of the same wall). I'm using TP-Link adaptors. I would just drill through the wall and wire the Ethernet directly but this is a rental apartment and I don't want to drill through walls here. What could be causing this?
Ethernet over power adaptors use the power line as a shared medium and superimpose a small (ie low amplitude/voltage), relatively high frequency signal on it thus anything that creates electrical noise on the line can reduce how well it works This could include a motor (so fridge for example)- I posit that these could even be external to you - ie if industrial loads are causing noise on the line before it gets to you.
I might try turning off everything and then seeing if the signal improves, then turning things on again. If this solves your problem, maybe adding surge supressors will help? To be clear, tjis is speculation and guessing.
You won't get 500Mbps. Whatever it says on the box that the adapters came in. That 1200 Mbps is a theoretical maximum speed. Users of powerline adapters, whatever the speed boasted by the maker, are lucky to get 200 Mbps, and most get much less. However, things to check include bad connections in the power circuit (inside the outlets); some appliances can put electrical noise conditions on the wiring, ones with motors such as washing machines, blenders, refrigerators, etc (try running these through surge protectors if they are in your apartment), and also items with switch-mode power supplies (phone or tablet chargers).