Atom uses lm317 and lm337 which are linear regulators. This is linear power supply. The wall wart is 220/110V AC in and 16VAC out and it's literally a transformer. The rectification and regulations are in the unit just like solderdude said.The Atom includes a SMPS, switching mode one. Linear power supplies are known to be better than smps, and most output DC, not AC. For example Topping sells a LPS for their DX3 Pro and D50 dacs.
Topping dx3pro d50 etc use 15V smps and 5V smps which are different from what atom uses.
Also there is no direct which is better. Best performing amps like thx 789 thx 887 hpa4 neurochrome hp-1 are all using smps. Hope this tells you something.