I have someone who will sell me a little router (cheap SOHO wireless router) but it needs a new power supply... does anybody know if there are shops around where I can get an inexpensive 3.3V, 3A DC power supply, i.e. that plugs into mains current, and how much they might cost? I want to know if it is really worth my while to get this cheap router, or whether getting a new power supply will cost so much that I might as well just buy a new router!

I suspect a replacement regulated power supply, of the type (specs) you describe, will cost almost as much as a complete new router.

Personally, I'd go the new router route, with its "total package" warranty.

waldwolf

Hunt the bargain bins / stalls at Pantip or Fortune Town , you can often find odd power adaptors around.