Inexpensive Headphone DAC

Audioquest Dragonfly Cobalt is a clear winner. 

They are based out of Irvine, CA but the Cobalt is made in China.

Topping E30 also very worth a look at $130. 

Yep. Modi 3.

Another vote for an Audioquest Red or Cobalt Dragonfly.  

The Topping D50 might be another choice, but it is more clinical sounding than the Modi 3, and more than twice as expensive.
IMHO, with the new AKM chip, the Modi 3 sounds better than the Sabre chipped D50.

Schiit Modi 3 or Modi Multibit if you have an extras 100.00.
I just got the Modi 3 to use with my Eddie Current ZDT Jr.
Sounds very good, especially for 99.00.

This isn't as much fun as getting suggestions - but a pretty good list of made in USA audio gear: https://americanmadeaudio.com/

I have an Audioengine and it's not bad at all.  Not sure where it's made. 

Or the Meridian Explorer 2 DAC which even does MQA decoding!
Full 24/192 and MQA for under $200.

It is likely assembled in China but designed in the UK I think.

Regardless I have one of these too and it is quite something for the price.

Any of the Audioquest Dragonfly models
Black, Red or Cobalt.

I went with the basic Black and it works extremely well for me.

ps: and don't just take my word for it - read the review by the Cleveland Browns fan who was multi-thousands USD into various DACs, and how the KTB stood up to those.

https://www.khadas.com/tone-specs

against: doesn't meet your not-made-in-china requirement
for: everything else.  note the DAC chip (ES9038Q2M).

Research 
SMSL VMV D1 DAC

AKG -HP 12U ... china but,really built.

Thanks for all the suggestions!

Wyred 4 Sound udac-hd https://wyred4sound.com/products/dacs/%C2%B5dac-hd
Excellent American made products!

Beresford SEG Dac

schiit.com...Modi Multibit / C Media USB $249 made in USA!