What is the power or voltage of this iPod?

I don't know if i've understood your question - so i try to answer both possible voltage things

as you could have seen in the teardown - step 12 - the shuffle has a 3.7 volt lithium-polymer battery with a capacity of 0.27 watt-hours

when you charge the shuffle via usb - it will get 5v from the usb with a maximum of 500mA.

the technical specs incl. the charging time are here

since i didn't find any specs for the usb power adaptor from apple - i can't tell you anything about it - except - it has 5v