The Black Friday sale on the PlayStation Store is live now, and alongside offering big discounts on games, the sale also gives users a chance to get a cheaper PlayStation Plus subscription. However, this only applies if you're a new customer or wanting to upgrade your subscription tiers.
New customers get 30% off PlayStation Plus, and if you upgrade from a PlayStation Plus Essential to Extra subscription, you'll get 25% off. If you make the big jump to Premium from Extra/Essential, though, you'll again get 30% off.
There's no mention of keeping the same tier for a discount on the PlayStation Blog, and while some people online are saying they can get a deal on their subscription without upgrading, it seems this deal is meant to attract new customers primarily.