Slow Powerline networking

I recently just bought a power line networking kit, the "Zyxel PLA407" to be exact, and a new graphics card. I plugged one of the adapters into the outlet next to my router and plugged it into the router, and I plugged the other in my room and into my computer. At first it was really slow, but then after 5 mins it got to a really fast speed and I was very happy, (11MB/s on speedtest.com before I put it in, then 20MB/s after I plugged it in). Then I powered down my computer and installed the new graphics card I got. After that the internet speed still says 20MB/s on speedtest.com, but on steam i'm downloading between 50KB/s and 800KB/s, I used to get 1.5MB/s - 2MB/s all the time before so I have no idea why this is happening. Does anyone know why this is happening? If you need any more information don't hesitate to ask.

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I don't have a solution to this, but I just bought this product off newegg as it was onsale for half off. I should be getting it Monday or so. I'll give it a whirl and let you know what I'm getting. I haven't heard very many good things about any of these powerline porducts, but this particular model got some very good reviews overall so I pulled the trigger and got a pair to check out.