Those little "wall-warts" are occasionally and notoriously short lived, though some will go on for years. Try another wall plug (even if the fuse/breaker is OK). Probably won't matter but couldn't hurt. Something with a large electric motor like a furnace circulating pump or vacuum cleaner in the same circuit can shorten their lives.

If that doesn't work, consider a Accu-Cycle charger/discharger or similar instead of buying another like that one.