The telco reversed earlier statements that there had not been a problem at the centre, despite reports from customers made to iTnews and to the Whirlpool broadband forum.
"At approximately 9.09am on Saturday 18th April the data centre experienced a partial loss of mains power due to [a] high voltage fuse failure on one phase in the City Power high voltage substation," the company said in a post-incident statement made to iTnews.
"At this time, the UPS systems commenced supplying power to the facility, as per their design. Within minutes, the back up generator set successfully came on stream.
"However, one section of the facility involving a small number of customers experienced an insufficient supply of power. During this time, [the] rest of the customers in all other areas of the data centre were maintained by the generator were unaffected and remained in service.
Power was restored by 11.45am although safety checks of the data centre subsystems continued until 2.20pm, Primus said.
When quizzed on why the generator was unable to handle the full data centre load, Primus chief executive Ravi Bhatia told iTnews the centre was between phases of a multi-million dollar upgrade to its power systems following an outage in February.
"We've redesigned the power systems completely," Bhatia said.
"Between two of the phases part of the data centre had a problem. It was just bad luck."
But several customers disputed Bhatia's claims that only a small number of customers - up to nine in total - had been affected.
"The idea that there's only nine customers in a room that size is crazy," said one customer, who spoke to iTnews on condition of anonymity.
"I think they've sold almost all the space in there, something like four rows of twenty racks each."
Bhatia said that despite the latest outage, from 8th May onwards the centre will be "beyond bulletproof."
This is when Primus expects to bring online the second of three phases of its power upgrade.
The first phase, already completed, saw the creation of the ‘extension' facility with three generators, located across the street from the main centre.
Bhatia said phase two completion will double the power capacity available to customers.
This means many will be able to add servers to their racks for the first time since the February outage, breaking a close to three-month cap on rack power.
The news will no doubt be welcome relief for customers that have been unable to change or add to rack configurations since February.
Bhatia also quashed rumours that roadworks in the street were behind the latest outage.
"My first feeling when I saw roadworks was that they'd dug up a cable - but the cause was a faulty fuse," he said.
Bhatia also denied suggestions that a newly asphalted strip running down the middle of the street was new electrical cabling between the old and new centre, as suggested on the Whirlpool broadband forum.
"It's a new water pipe, 30cm below the surface," he said. "The multiple ducts we have are a metre below that."