Well, close, but I would get one that already had an eqtype in the label to make it a hair easier.
Just be careful, the name of the label needs to be unique otherwise you will get a duplicate name xml error in game.
Kinda like this.
<Label item="MyPowerPecentLabel">
<RelativePosition>true</RelativePosition>
<Font>2</Font>
<Text>100</Text>
<TextColor>
<R>255</R>
<G>255</G>
<B>255</B>
</TextColor>
<EQType>360</EQType>
<NoWrap>true</NoWrap>
<Location>
<X>5</X>
<Y>5</Y>
</Location>
<Size>
<CX>20</CX>
<CY>12</CY>
</Size>
</Label>
You would rename the label to something more appropriate, edit the location X and Y to be where you want it to show and don't forget to place the <pieces></pieces> tag at the end of the XML to call the Name you gave the label. (ie: <pieces>MyPowerPecentLabel</pieces>). When placing the names at the end of the file, it does look at what piece is 1st and so-forth since items are Layered. So if you want to make sure the percent is on top of everything else, place it at the top of the Pieces list.