Best Desktop Speakers under $500

Logitech makes some good speakers for computers check out this link https://www.logitech.com/en-us/products/speakers/z906-surround-sound-system.980-000467.html enjoy 

Find a used pair of Adam A5. Active. Ribbon tweeters. Better than all of the others I have had (lots of computer speakers, home audio monitors {Polk, Dynaudio, ...}, Monsoon planars, Audioengine, Swan M200 various versions). Each of the above did good things.

The Adam A5's do a lot of good things. The bass is very good and the ribbon tweeters are oh so good in a nearfield desktop system.  They can also play loud enough to fill a small room if you are not at your desk. 

Use an external DAC if this is a computer based system

OP, I assume you mean powered speakers but please clarify if that assumption is incorrect.
I would say the SVS Prime Wireless, Vanatoo Transparent One Encore, Edifier S2000MkIII, Kanto YU6, and Audioengine A5+ (Plus) are the better choices at that price point.

Mine. ;)

1. Edifier G2000 Stereo Speakers.
2. Logitech Z207 Bluetooth Computer Speakers.
3. Cyber Acoustic Portable USB Laptop Speaker.
4. Bose Companion 2 Series III Multimedia PC Speakers.
5. Cyber Acoustics CA-3810 Computer Speakers with Subwoofer.
6. HP Gaming Speakers X100