How can I get ultra clean dc wall power for my arduino project?
This is what I use, although admittedly not in your application. I run it from a 12V wall adaptor and adjust the output voltage to suit my requirements. The input should ideally be at least a couple of volts above the output(depends on current and temperature at 25degC and 20mA it's > 1.6V and 1.5A at the same temp it's > 2.7V).



Another alternative if you want to really go to town would be to repurpose an old computer ATX or similar PSU. There are plenty of guides out there and it's a straightforward job.