I never opened it.
I bought it a while ago and completely forgot about it. I originally bought this PSU for a PC upgrade I was planning. However, my plans changed completely when I decided to purchase an entirely new pre-built computer instead. Because of this, the power supply was never installed or used and has simply been sitting in its original box.
Your Listing Description (English)
Okay, here are a few options for your listing description, incorporating your situation. I'll give you a main option and a slightly shorter one, both designed to be clear and build trust with potential buyers.

Option 1: Detailed & Trust-Building
This option clearly explains the situation and emphasizes the "new" condition.

"For sale: Vortex 800W 80 Plus Standard Power Supply Unit (PSU) - Brand New, Never Used!

I originally bought this PSU for a PC upgrade I was planning. However, my plans changed completely when I decided to purchase an entirely new pre-built computer instead. Because of this, the power supply was never installed or used and has simply been sitting in its original box.

I'm moving soon and need to downsize; this deal is only available until midnight on June 12.
When you call please mention you found this ad listing on OKz.ca