Funny. HTC says
HTC Mobile Phone Support - HTC EVO? 4G (Sprint) - Power and Battery
What can I use to charge my phone? close
Only the AC adapter and USB sync cable provided with your phone should be used to charge the phone.
I still think it is a combo of charger cables and charging ports. Given my situation with owning 3 EVO's, and how 2 HTC charges only work great on 2 EVO's but not wifes at all... 3rd HTC charger doesnt work on any of 3 phones - feels very loose on all 3. Samsung charger snaps into place on all 3 fine. Well, needs slight messing with for wife's.