In reply to Kemics: I train power endurance by doing 4x4's. The exercise is similar to what was mentioned above, just longer and more intense.
First of all you need to find a problem roughly 1 grade below what you are climbing. For example, if your a v6 climber (F7a) you need to find a v5 (f6b+/c).
You are then going to attempt to climb the route four times in a row, attempting to not fall off.
However, while climbing the route you need to time yourself to see how long it takes.
If it takes you 4minutes to climb the route four times, you will then allow yourself four minutes rest.
Once the rest time is up, you repeat the process again! You will do this four times, so you will climb or attempt the problem 16 times.
Once complete rest for 10 minutes.
In the 10 minutes find a problem which is 3-4 grades easier. (f6aish).
Once the 10 mintues is up, repeat the process again on the new chosen route.
If you have any more left, attempt a 3rd route, just make it easier! You be surprised how your find v2 hard at this point!
Personally if the set takes me over 5 minutes (7 minutes for example) i will only allow 5 minutes rest to keep the intensity up!
Furthermore take notice of potential rest hold on the way up! The only time your going to have t rest while performing the set is on the wall. Finding a rest position may allow you to climb the problem that extra one time due to a good shake out! Plus it helps finding rests on sport routes
Just a quick note, if you are beginning to fail at climbing the route massively, use an extra hold or two, but make sure there small and don't decrease the grade of the problem by like a grade! Otherwise there is no gain!
This was the training method i was taught, and ive defiantly felt a difference and i would recommend it to anyone wishing to train power endurance. Also remember, i only do this twice a week due to its intensity, if you ever feel anything twinge jump off and leave it for that session!
Hope this has helped! Any info drop me a message
Jim.