Doug's Musical Ability, in GURPS

[Shepherd]

Shepherd wrote:

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Look more closely at the write-up. Ultra Power merely provides rules for pulling power stunts with your other powers, it grants no powers by itself. For example, if you've got super speed, you can use Ultra Power to try to disarm fifty bombs in one second even if a strict reading of the power indicates that such a task would be impossible.

Not quite.  You must have a power talent, but not any abilities.

Supers, pg 112 wrote:

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To do this, a hero must have a power talent, and must have taken the advantage Ultrapower (see p. 30). Then the player describes the feat he wants to accomplish

He doesn't have to have any powers, just "Musical Power Talent."  And, if you check the Latent Powers section on the next page, it is a bit more clear:

Supers, pg 113 wrote:

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Since the system for one-use powers relies solely on Will and Talent, and not on any abilities of a power, it’s also suitable for characters with latent powers (Talent but no abilities) who are only capable of the occasional amazing feat of power because their full potency has not yet developed!

I mean, that sounds almost exactly like what Doug does.
    

Actually, that doesn't sound like what Doug does. The operative term is "the occasional amazing feat of power." Doug's power songs are not an occasional thing. He uses them during practically every battle, and sometimes even uses them outside of battle. Ultra Power is meant to simulate performing unique extraordinary tasks that are thematically related to things that you can already do, not as a way to perform the same set of tricks over and over.
The write-up for Ultra Power specifically states: This new advantage is based on Gadgeteer. The intent is to let characters get creative with their abilities without having to sink an absurd number of character points into covering every single thing which you may possibly want your character to do. Your modifications are like trying to make a gadgetmaster who cannot possibly fail to produce whatever gadget he desires.
On the other hand, I do believe that a modified version of Ultra Power could make a good method for having Doug learn new power songs. While the advantage usually only gives you the option to spend character points on an ability that permanently replicates the attempted oneshot feat when you score a critical success, you could create a 50% Cosmic enhancement that lets Doug do so every time he successfully attempts to learn a new power song.
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"Anyone can be a winner if their definition of victory is flexible enough." - The DM of the Rings XXXV