An electrical problem between Wandsworth Common and Clapham Junction on Thursday caused services in and out of Victoria station to be suspended.
Network Rail said services were back to normal at 08:00 BST.
A displaced conductor rail caused damage to six trains on Thursday, leaving commuters stranded for up to five hours.
Emergency services were called in to rescue passengers on some services, with the London Fire Brigade helping about 900 off non-moving trains.
Police and paramedics also brought water on board some trains for those who had been stuck inside without air conditioning.
All Gatwick Express services were cancelled and passengers on Southern trains were badly affected.
Train services through south London have resumed after a power cut which left thousands stranded.