At the risk of oversimplification (which this is) a power amp is essentially a modulated power supply. In that context the best amps* I've heard all have large linear power supplies. As regards the ultimate power needed, all things being equal, a good big amp will beat a good small amp, but in the real world where budget constraints apply, room size, speaker choice and listening level will influence choice.
* I haven't critically listened to any tube amps above 100 wpch.