The top speed between the devices is 14 Mb/s, so they will never attain the 20Mb/s speed you had with you router / modem.
Netgear offers this FAQ for Powerline devices:
Problem:
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Workaround:
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- Powerline products work better when plugged into the wall without
power strips, extension cords, surge protectors, or uninterruptable
power supplies.
- Passwords. Powerline products have both a network password, and a
device password. A particular device's password, which is not
changable, is printed on the Powerline product label. Once you have
collected all your Powerline device passwords, use the encryption
dialog box, as described on pages 9 and 12 of the XE102 User's Guide,
to change the network password. (Without password protection, it is
possible, although unlikely, for someone very nearby to access your
network.)
- If you changed the default network password, make sure that all the Powerline products use the same network password.
- If you've moved a Powerline unit, or disconnected the cables, your
other network devices may need about 5 minutes to refresh their
information about the Powerline's current status.
- If you have earlier Powerline products, switch to the encryption
used by later products. (Early versions of XA601 and XE602 are known to
have compatibility problems with newer models.)
- To test whether a house's electrical wiring is contributing to
Powerline problems, plug units in the same room. Examples of potential
problems are:
- Old fuse boxes.
- Old wiring that does not meet modern wiring building codes.
- Swap devices to isolate the problem to a particular Powerline unit.
- Reset the Powerline adapters to the default settings using the utility.
- Use all the same Powerline models for best connectivity. Also,
software for one model may not work for another model. In particular,
remote and advanced features may not work between Powerline
manufacturers.
- Powerline is not directed at businesses, however it may work in a business environment, anyhow. See Assessing Powerline for Business Environments.
In some cases noise can be limited by placing line conditioners or
surge protectors between the source of the noise, and the Powerline
units. (Not between the units.) Consult a professional electrician to
evaluate your electricity's noise and to suggest remedies.
