Can I use V brake levers for U brakes (side pull calipers)? I accidently bought a V brake set instead of U brake set (side pull calipers) for an old bike I'm fixing. 
I really like the levers and would like to keep them.

These are the levers I've bought:
XLC BL-V05 Disc Brake Lever for V-Brake

Are V brake levers in general comaptible with U brakes?
I found this helpful site which explains the different types and compatibilities:

Mechanical bicycle brake compatibility


  
  Types of brake levers and calipers
  
  
  These are the brake lever types with their amount of cable pull per
  full lever travel (about 20 degree angle):
  
  
  V-brake (also known as Direct-pull, or linear-pull), 15 mm
  Cantilever (also known as center-pull and direct pull), 7 mm
  Old road, 7 mm
  New (SLR and Super SLR) road, 8 mm
  
  
  Here’s a list of mechanical caliper types with their ideal amount of
  lever cable pull:
  
  
  V-brake (also known as linear pull brakes), 15 mm 
  Mini V-brake, 7 mm 
  Cantilever (also known as center pull brakes), 7 mm 
  Old  road calipers, 7 mm 
  New road calipers (SLR and Super SLR), 8 mm 
  MTB mechanical disc, 15 mm 
  Road mechanical disc, 8 mm 
  U-brake, 7 mm 
  Roller brake, 7 mm
  


Conclusion

Regular V-Brake levers are not comaptible with U brake calipers