Companies like Antec and Corsair do exactly what many, many other companies do when they want to enter a market but don't want to invest in expensive production facilities, they contract the work out.
Say Company "C" wants to enter a market, say power supplies. Company "C" thinks it sees an untapped market within the overall power supply market and believes it can expoit it.
OK. First, hire some competent engineers for design work. Now what? Build a factory? Expensive proposition and slow to get product to market.
Instead, they have their engineers and design team draft a set of requirements for their proposed power supply and approach some true manufacturers of power supplies with the specs and invite the manufacturer to bid on building it....cost per unit.
Company "C" gets back samples of what the manufacturers think is the answer to the spec requirements, then chooses one. Then Company "C" goes to chosen manufacturer "S" and begins to work more closely with them with tweaks needed to the unit, set final pricing per unit, length of contract, etc.
Company "C" then, at a specified time, begins receiving final production units that are shipped out for sale with "C's" name plastered on them, despite being a Company "S" product. And this happens all the time in almost every facet of manufactured goods....tires, computer parts, medicine, food, you name it.
A company just lets bids to manufacturers for product, picks one of the samples returned for evaluation, then contracts for "x" amount of items over "y" length of time at "z" price per unit.
The company that is buying the product typically has all the say in how the product performs, a bolt, a tire, a power supply, but rarely has much say about how it's made....that's left up to the manufacturer to decide. And that's why the old PC Power & Cooling Silencer 750 internally is almost identical to the old Corsair 620HX.....both were based on the same Seasonic platform, albeit with small tweaks to meet power output requirements for the specific units and meet electrical specs---ripple/noise generation (a PCP&C strong point), voltage regulation, etc. If you couldn't read part numbers for the individual parts in the chassis of both those power supplies and were just looking at the two units naked, side by side, you'd probably not be able to see the difference between the two.
Antec does the same thing. Lets bids on a proposed unit, contracts what it feels is the best overall unit for the cost. Unfortunately, one can take the cost per unit too far, as Antec once did, and ended up having crap capacitors being used because it saved a few pennies per unit.....and when you move a million per year, those few pennies can add up---until the cheapness comes back to bite.