New to the boards and I'm currently building my first "real" rig. i am using the Thermaltake 20 GT RGB case, Gigabyte z390 motherboard, 9900kr chip, 4133 patriot memory, EVGA Kingpin Card (currently looking for EVGA Kingpin hydro copper water block as I don't have yet) Bykski Kingpin water block, Thermaltake custom water cooling kit with a 360 and 420 radiator both over 60mm thick and a ton of Thermaltake ring 2 fans. I am a little disappointed that the case cam with 2 usb 3.0 connectors and most motherboards only have 1 USB 3.0 connector and I don't have a solution to fix this. Please give any advice on this as I'm currently getting parts in and about to build it. Also this is my first time doing water cooling so any advice there is very welcome also. Thanks!

Is there a usb 3.0 to usb C converter as I am out of USB plugs but I do have that plug still available.
 

If you need more internal USB headers, look at the HUBBY7.  Great device as I use two of them chain back to back since my MB only has 1 USB 2.0 header.  I know shocking. lol
 
If you need more external USB 2.0 headers, just grab a simple hub.  This is the one I use and works great.

It just sucks not being able to use all of the USB plugs on the case due to this whole case having two usb 3.0 plugs.

flyinion

Fuzzypunks
It just sucks not being able to use all of the USB plugs on the case due to this whole case having two usb 3.0 plugs.

It's not the case's fault though, many motherboards have 2xUSB3 headers but it's a newer thing (and only newer case designs support it).  MSI and ASRock both have Z390 boards with dual USB 3 headers.  Gigabyte has them for X570 (and maybe MSI I don't remember offhand).  I was originally going to go with the Gigabyte X570 Master but ended up with the Asus.  I didn't lose out on ports overall, they just moved them to the rear I/O instead of an internal header but yeah now I have a set of unusable front panel ports myself.  Like I said, I'd totally buy a USB 2 header to 3.0 front panel adapter if I could find one that is for sure reputable, but I'm not really looking to blow up a $350 motherboard with a $10 adapter cable of questionable quality.

Yeah, my Phanteks Enthoo 719 (nee. Luxe 2)  has 4 x USB 3.0 & 1 x USB type-C front ports. I tried using a USB 2.0 -> 3.0 adapter on my Z370 Classy but no devices registered when I plugged USB keys in. The end result was I simply ordered a couple USB 2.0 silicon dust caps from Amazon to plug the non connected 3.0 ports and save any confusion. Not really an issue as I cannot see a point where I absolutely- positively need more than 2 devices plugged in at once and if that became an issue, I can quite easily access the rear USB ports.