AS OF XPERL 3.5.0 (15th Aug 2012) THIS FIX IS NO LONGER REQUIRED AS THEY HAVE PUT THE DEFAULT BAR BACK! WOOP!
THANKS ALL !
If it gets changed again I'll re-activate this addon, otherwise there will be no more need!

OLD DESCRIPTION FOLLOWS:

I love X-Perl, it's a great looking addon.
Thing is, I'm a Holy Paladin, and the 'yellow triangles' which are 'not a bug' I find inadequate and the X-Perl authors don't seem to get that some of us Paladins really don't like them despite many posts on the wall.
I stuck at using the old version of X-Perl until now but it really was time to update it.
I could get another addon for my HP bar, I could move away from X-Perl, but you know what? I don't want to, I like how it was. It worked.

Anyway, this gives those people the chance to get the Blizzard UI PaladinPowerBar back attached to their XPerl_Player frame, and it also stops the yellow triangles working.

It's very basic, you will probably get a flash of the three yellow triangles before it works, or in some cases it may only work once you generate a Holy Power, though on my setup it seems to just work as soon as I log in.

I wrote this for me, but I know others want this functionality so I'm sharing it.
If you want anything else you'll have to code it yourself.

Notes:

If you run this and you are not a Paladin, it will do nothing and disable itself.
If you run this and you do not have XPerl_Player running, it will do nothing and disable itself.
This only works with the latest version of X-Perl.
It has not been tested for levelling Paladins, but if your HP bar doesn't appear when it should just reload the UI and that should be fine. As I said, it's basic.

I honestly hope that this addon will not be needed in the near future, and that the X-Perl guys will put their own code back into the current version and give us the option of Blizzard PaladinPowerBar or yellow triangles.

X-Perl PaladinPowerBar Fixer