OK, this should be repetition of what you already know, but here goes:
Powerline 101:
All powerline adapters quote symmetrical bandwidth, so gigabit wired connections would be 2Gbit. Anything other than gigabit class adapters come with 100Mbit ports.
With powerline you avoid surge suppression, so plug it directly into a mains socket, not a spur socket, also your sockets need to be on the same circuit ideally. They don’t handle circuit jumps well - sometimes they will be OK, but it’s a crap shoot (look at your fuse box, if upstairs and downstairs sockets are on a different breaker, then expect problems).
Update firmware - it’ll be the same tool usually that you used to change the default encryption key, but it will also give you insight into the reported sync speed between devices.
Ultimately, powerline isn’t something you use if you have any other option, even if it’s a PITA to run cable, it’s still the default answer.