Sorry, Never seen anything like this... Nor do I think it exists, it would require extra internal cabling and I do not think there is high enough demand for anyone to make this - it just wouldn't be cost effective.
Update to comments -
I am not saying it is impossible, but... USB networking sucks which would be the easiest implementation (from PSU to internal USB header). For descent networking, it would either have to have a new dedicated section on the motherboard or have a dedicated internal card/link to PCI/PCI Express.
Next (and probably most importantly) - Cost! Testing and licenscing for official HomePlug "Status" costs and I doubt you will be able to release a device for under £10-£15, this will greatly increase the cost of a PSU when probably less than one in a thousand people actually would buy it (Wired is probably 7-8/10) and Wireless the majority.
With regards to Apple - Again, I doubt there is a big target market - On top of this, I do not think it is worth investment - if you start with what I wrote above, I think that within the next 10 years, we are not going to see wired connections on home machines (I hope I am wrong!).
The fact is (talking home users) - Most machines now have at least gigabit cards whilst nearly every home user only has 100Mb Routers/Hubs/Switches. Nearly everyone wants internet speed but rarely actually copies files from machine to machine over a network (most people either do not do it or use USB sticks). Because of this - and the fact that wireless is getting better, I just think that wired will be phased out and 10 Gigabit wired connections will be the standard for business machines and available on premium consumer equipment.
Said rather a lot here! I hope someone finds it interesting!