Power Line adapter - would a pair of these be any good ?
We have HP Procurve switches and use those splitters in a number of places, they work best for us just leaving them on auto negotiate. If you are going to set the switch to manual settings, make sure you set the printer and computer to manual rather than auto.
None whatsoever, does the computer get a network connection from both sockets on the economiser?
Does the printer get a valid ip address ie not APIPA etc, or have you manually configured the ip address, subnet mask etc onto the printer and done a DHCP Reservation in your DHCP Scope etc using the printers mac address
When it is connected using these splitters, can you ping the printers ip address from a computer on the same subnet / vlan etc ?
You adding the printer on a print server or onto a client or what exactly ?
Which drivers are you using on the print server and for the clients ?
I suppose if it loses its static settings then a reserved address will be good if it goes looking for a dhcp address.
We have PCs and printers on our networks and they do work. We only use them when we have no other choice [staff moves occasionally mean that there are not enough outlets in an office]
We did see a circumstance where the printer would not connect to a split cable but a PC would. After some head scratching we limited the port speed where the printer was to be connected [100 Mb] and everything returned to normal.
Do you use VLANs, you might have the wrong VLAN set as untagged on the port.
I may have read this wrong but you cannot plug one of the splitters directly into a switch and use it that way, they can only be plugged into panel or sockets and split that way. If your switch is full you will need to get an additional switch.