the quickest thing to do, to make sure you get a replacement for your live performace, would be to contact your nearest Line 6 official service center. http://line6.com/service_centers/
or alternatively you could call LIne 6 UK if you're in Europe, or LIne 6 US if you're outside europe. their numbers are available from the contact us link at the bottom of this page.
I'm sure you'll be able to get a new PSU asap, but please come back and let us know how you get on
I hope this answers your question
i would recommend buying one....
pursue the replacement of course... but then you'll have a backup.
as well as having it up and working potentially sooner....