what is modular power supply?

Yep.

Ideally I prefer "Semi-Modular" which has the main 24-pin power cable permanently attached. This should be slightly more reliable, and since you always need this cable there's not a lot of advantage to fully modular.

I bought a Semi-Modular for my dad's PC to reduce cable clutter. He has no graphics card so the only cable he needed was one for his SSD and HDD's.

(cable clutter is especially important in small cases, or even in large cases to avoid blocking air flow.)

In fact, if you only used the M.2 slot on the motherboard and nothing else you'd only need the main power cable.
 

Wing0

Reputable
Nov 5, 2014
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Non Modular - all cables are permanently attached to the psu.

Semi Modular - Only the cables you need (+ a few more maybe) are permanently attached. The rest you can unplug.

Modular - All cables can be unplugged
 

norseman4

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Mar 8, 2012
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As stated, a modular PS allows you to use only the cables you need, keeping cable clutter to a minimum. Additionally for many models you can get cables of different lengths from either the manufacturer or a third party for specialty builds.

In a Corsair Obsidian 250D, or any mITX case that accepts a standard ATX power supply, the cables are much longer than required. Alternately, a super tower monster could easily make you want for longer cables.