[dreamcompiler]

The power supply. An AC-to-DC converter is bigger, hotter, and more prone to failure than a much simpler 24VDC buck.

[Johnny555]

Aren't efficient DC-DC converters just switching power supplies? Are they inherently more efficient or long lived than a 120VAC-DC switching power supply?

I'm using my ipad while plugged into a 120V USB charger, and the charger isn't even warm.