Although they have (mostly) common chipsets, the innards of this group of adapters were quite different. Figure 6 shows the top of the Cisco Linksys PLE300 board. A Realtek RTL8201CP provides the single 10/100 Ethernet port and you can see one of the two RAM chips that provide 16 MB total.
Figure 6: Cisco Linksys PLE300 board
Flipping over the board (Figure 7) reveals the second-generation Atheros INT6300 chip. The part number is partially obscured because the INT6300 sits snugly against a thermal pad on the bottom of the case, which left some residue on the parts.
Figure 7: Cisco Linksys PLE300 board bottom
Figure 8 shows the four-port PLS300, where a Marvell 88E6060 6 port 10/100 switch occupies the same space as the PLE300's Realtek RTL8201CP.
Figure 8: Cisco Linksys PLS300 board
The Plaster Networks AV200 in Figure 9 uses the third-generation Atheros INT6400 / INT1400 chipset, with a nice finned metal heatsink on the INT6400. An IC+ IP101A provides the 10/100 Ethernet port and a single Etron EM639165TS adds in 16 MB of RAM. Rounding out the basic design is 2 MB of flash tucked away somewhere (a common feature to all designs).
Figure 9: Plaster Networks AV200 board
Figure 10 shows you what your extra $20 buys in the Plaster Networks PLN3. I wasn't able to find a way to easily get this apart without risking damage, so I'll just have to guess that it uses the same powerline parts and adds in a network processor, a Marvell Shiva, perhaps?
Figure 10: Plaster Networks PLN3 inside
Moving along to the NETGEAR XAV2001, we see what looks like a pretty clean layout, with memory and Atheros INT6400 / INT1400 clearly in view in Figure 11. But packed under that board is a whole pile o' power supply and powerline interface parts. The Realtek RTL8201CP 10/100 Ethernet interface is on the bottom of the top board and 2 MB of flash is squirreled away in there, too.
Figure 11: NETGEAR XAV2001 board
Speaking of packed, I opened up the XAV2501, took a peek and closed it right back up again without bothering to snap a photo. NETGEAR tells me that it uses the same powerline board, which appears to be buried under a few layers of power supply, powerline interface and components for the filtered outlet.
Rounding out the group is the nice, clean layout of the TRENDnet TPL-303E in Figure 12. All the usual suspects are here, INT6400 / INT1400, IC+ IP101A Ethernet and 2 MB of flash and 16 MB of RAM on the back of the board.