Did the switch/hub have a power supply originally?
If it did then presumably it no longer works or you've lost it and you need a replacement.
Shouldn't be a problem you can get multi-voltage DC power supplies, I believe Argos may do them.
They also come with many different connectors so you should find one to suit your hub/switch.
Make sure you get the polarity right, this should be marked on the Linksys, by the power socket.
Also make sure the PSU delivers at least 200mA.