I just bought a new racket, and the tension is 26 lbs, my playing skill is average, sometimes feel like this racket is consume more strength and energy compare to my old racket which is 24 lbs, not sure is the racket itself problem or the tension problem or my problem.

new racket is Li Ning UC3100
old racket is Yonex Carbonex 8

my yonex Cab 8 buy 1984..
nothing to do with racket..
you still not good enough
the power come from your hand

It just means you aren't strong enough to handle the 26lbs, yet.
Slowly work on your shoulder, arm, forearm, and wrist strength.
You will find playing with higher tension gives you better control over your shots.
Smashes will be faster, drop shots will be steeper, and net shots will be tighter.
And best of all, the sweet sound of a full-blown smash, is much much sweeter on a high tension-ed racket.

Also, string tensions drop over time, work the 26lbs strings alittle, it should drop down to 24lbs or 25lbs in no time.

Me personally favours 29lbs or so, but since there will be a drop in tension over time, i usually string mine at 30 or 31lbs, if the racket can take it.

seems my arm still not powerful enough

Thank for your advise, uncle_ben
is that mean increase tension base on our strength?