broken Amplifier plu

Hello,

We have a coaxial cable coming out of the wall attached to an ac adapter. Today the plug to the ac adapter broke and we have no service. The cox store, best buy, nor our local Walmart carries them. I contacted COX via chat and they said "they don't provide replacements." Why doesn't my internet work without the amplifier plugged in!? How can I get a new plug?

Thanks in advance!