ethernet from a power outlet

Amazon has a number of devices which allow for Ethernet connectivity thru a power outlet.  How do these compare with a plain Ethernet jack?  I want to do some hi quality streaming but I do not have a jack near my stereo system and I'm told that WiFi is not as good sonically as having a hard connection.
WiFi is better than nothing, and if you find an unused channel and good signal strength really good.

Networking over power is no panacea. Distance issues, noise and interference can all occur, plus you are putting digital noise directly into your power. Now that's more noise you have to filter out. 

Your best bet will still be hard Ethernet cables to ensure the best streaming experience. 

Route any network cables away from your interconnects and power if you can.
I used this in two locations for a desk VoIP phone and experienced major timeouts. Definitely would not use this solution for extending audio streaming.
I use it at home (granted, I'm in an apartment), and have a very reliable 80mb throughput. No noise issues that I can discern.  Has to be on the same breaker box.
I have had fabulous results. Better than I ever anticipated. I'm getting far superior sound quality to years ago when I had up to $10K CD players in my room. 

I'm using SONORE Signature Rendu SE and Small Green Computer via an Audioquest Ethernet cable from the wall outlet IOP converter to the digital front end. This has proven to be a beautiful digital front end. 

Lately the digital/amplification is crushing it, sensational results with the EXOGAL Comet DAC and Ion PowerDAC with upgrade HyperDrive. I just recently wrote about the upgrade to the Ion, and I did not overstate the improvement. It's terrific, and makes the Comet and Ion the best DAC/Power scheme I've used to date bar none. VERY high end sensibility for about $7K. Not chump change, but more erudite than any big gun separates DAC and amp (stereo or Monos) I have used. I suspect that with time I will best this performance, but in my experience it would take a lot more MSRP firepower to do so. 

I have done servers in the room previously with hard connection and the sound quality I have now supersedes those setups. So, IOP is certainly not holding back the system from attaining excellent results. I am using the basic two unit set available from Best Buy for converting the signal from the router to power line and back again. Occasionally there is a handshake issue, it seems and it takes a few minutes for signal to get locked in, but once established I'm good to go. 

(SONORE, Small Green Computer and EXOGAL products reviewed by myself for
@douglas_schroeder What IOP devices are you using?
I tried one and it worked perfectly.
noromance, I'm using the Netgear Powerline 1200. Bought it at Best Buy for well under $100. Terrifically helpful devices for me, as I built my listening room so robustly, with resilient channel enshrouding the framework, such that I cannot get a good wireless signal to penetrate the room! So, this is a huge blessing. I'm so happy the sound quality has been able to exceed what I even accomplished prior. People may speak theoretically about such things as powerline noise, or such setups being worse than wireless, but not in my case, not in actual use. Thankfully!
@douglas_schroeder Thanks. Very helpful post.
These powerline devices are very convenient and from my experience, very stable and reliable.  I can't detect any audible noise when I use them for streaming as well as for video streaming.  I have been using cheapo(less than $25.00 ea if I recall) Diamond Multimedia HP500AV models for about 4 years now with no troubles at all.