RAN 1.35v vs 1.5v

I wanted to get more RAM for my newly-acquired PC

Entering the make and model, HP EliteDesk 800 G1 Small Form Factor

Crucial suggests only CT2K102464BD160B

DDR3 PC3-12800 • CL=11 • Unbuffered • NON-ECC • DDR3-1600 • 1.35V •
1024Meg x 64 •       $76 even cheaper at NewEgg,  


Kingston suggests only KCP316ND8/8

Specs: DDR3, 1600MHz, Non-ECC, CL11, X8, 1.5V, Unbuffered, DIMM,
240-pin, 2R, 4Gbit   $98


The items are in different order but the main difference seems to me to
be  1.35v vs 1.5v.   

That seems important, right?  How can they be different for the same
computer?   (I'm not really concerned about price unless they could sell
it cheaper by making it at the wrong, lower voltage. )

Do I need to look up what the computer puts out?   Would one of these be
overclocked if the computer puts out 1.5v and the other underclocked if
the computer puts out 1.35? 

I already have 2 sticks,  Do I want to get the same voltage that they
use, whatever that is? 


   ------

Other differences are 
  Crucial says PC3-12800 but Kingston doesn't include that.  

  Kingston says X8, 2R, 4Gbit but Crucial doesn't include any of that. 

Does any of that matter? 


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FTR, I only looked at Newegg because Crucial was out of stock. NewEgg
says "Ships from China. Newegg Most customers receive within 10-32
days."

Hmm.  At
https://www.newegg.com/crucial-16gb-240-pin-ddr3-sdram/p/N82E16820156047
it says sold and shipped by Ram-Store and when you click on 12 New from
$88.46 , it goes to the bottom of the page where they have 12 vendors
selling the same thing.  Just like Amazon does it. I only looked at the
first 5 but one is in Hong Kong and "Most customers receive within 4-17
days.".  One is in the US and "Most customers receive within 7-9 days",
all except Hong Kong for the same price!! (For Hong Kong and the next 7
the price gets higher.)

But this doesn't matter until I understand the voltage question.