The fire at a high-voltage substation outside Paris brought traffic at Montparnasse to a standstill shortly before noon on Friday.
While electricity was restored in the late afternoon Monday, state rail operator SNCF said only two-thirds of the roughly 230 scheduled trains in and
out of the station would operate on Tuesday.
A complete return to normal will not be seen for several days because the maintenance facility for high-speed TGV trains was also hit by the power
outage, leaving many locomotives out of service, SNCF said.
Montparnasse, France's second-busiest station for high-speed train traffic, is a main departure point for holiday destinations.
The weekend was one of the summer's busiest with millions of people returning from their July vacations and millions of others taking to the roads, rails and skies for their August break.
The trains that did operate from Montparnasse were often packed solid, with hundreds standing in corridors for trips taking up to several hours longer than usual.
Scores of trains were cancelled over the weekend, stranding thousands of people in sweltering stations across western and southwestern France.
Others had to be re-routed throughout the weekend, often with hours of delays.
Grid operator RTE drew the government's ire when it warned that power might not be fully restored until Thursday.
The cause of the blaze remained unknown on Friday, though RTE ruled out arson.
On Monday, agents could be seen distributing coffee and bottles of water to weary travellers at Montparnasse.
While many were taking the disruptions in stride, often thanks to text alerts and updates, patience was wearing thin for others.
“Our train from Montparnasse was cancelled. We were told to get one from the Gare d'Austerlitz but there it was cancelled again,” said Nicolas, a pensioner travelling with his wife and their grandson.
Speaking to AFP about her dealings with exasperated clients, one agent said: “We can obviously see that passengers are fed up. Waiting for hours like
this is certainly not a picnic.”
The SNCF is urging people to postpone trips if possible, while offering to reimburse travellers who opt instead for the company's carpooling service Idvroom.
Montparnasse has suffered a series of service cuts in recent years, in part the result of insufficient network investments in recent decades.
The latest power outage comes nearly a year to the day after an electrical problem at an SNCF signalling station paralysed traffic for three days just as thousands were hoping to start their holidays.
Last December, the station was totally shut down for a day after a computer glitch during an IT update to signalling systems.
The government has promised 3.6 billion euros ($4.2 billion) of infrastructure spending over the next 10 years as part of an SNCF reform plan pushed through this year — which prompted weeks of strikes by rail workers.