Uh, Watts are a unit of power, i.e., energy per unit time. Specifically, a Watt (and it's capitalized, like any other SI unit named after a person) is defined as a Joule per second.
A "Watt per second" would be a measure of change in power. A Joule per second squared, in effect.
Incidentally, a "Watt-second" (some defibrillator charge indicators are so-marked) is exactly equivalent to a Joule.
Oh, and in electricity, a Volt is defined as a Joule per Coulomb, and an Ampere as a Coulomb per second. So if you multiply EMF in Volts by current in Amperes, the Coulombs cancel, and you are left with Joules per second, or Watts.
Or to paraphrase my high school physics teacher, unit analysis is your friend.
The fact I used 'per second' in my sentence is not technically inaccurate though.
Sure, when we describe something in Watts for example, the term per second is implied... but stating in the same sentence 'per second' is a mere redundancy in that case, not technically inaccurate.
It just means the sun's output is constant every second ... I didn't mean it like the sun's power output is increasing 384.6 yottawats every second (because that was/is not implied).
It simply means that for example, in 2 seconds, the sun would have generated a total of 769.2 Yottawats... but the Sun DOES in fact generate 384.6 Yottawatts every second.