Will a PS 300 provide enough juice?

No it won't.

No, it will certainly restrict dynamics and make it sound rather flat if it works at all. The 300 will work fine for your front-end gear, but not for a tube amp even of this size.

Thanks everyone for your response, most helpful. In short, I'am looking to regulate voltage on a tight budget. Looking at PS products(used) and Furman. Any other recommendations?

http://cgi.ebay.com/SOLA-MCR-1000-Mini-Micro-Computer-Regulator_W0QQitemZ380122822518

Probably too noisy for the living room. Best way is using a hard-wired unit in a non-occupied room (garage, basement ...) and dedicated line. Used portables like that can be found dirt cheap though. I have the same for the plasma that draws over 600W.

Wouldn't generally suggest under 2KVA to supply an amp but the "One" only draws 300W.

VA is more important than 'watts'. Especially as PF (Power Factor) drops.