Global Site Tag and Adwords/Analytics - gtag.js

Question

We are using Google Tag Manager on SOME of our sites, but not all. On the others, we are using the Global Site Tag (with UA-), like below:
<!-- Global site tag (gtag.js) - AdWords: 1234567890 --> <script async src="https://www.googletagmanager.com/gtag/js?id=AW-1234567890"></script>
<script>
window.dataLayer = window.dataLayer || [];
function gtag(){dataLayer.push(arguments);}
gtag('js', new Date());
gtag('config', 'UA-1234567890');
</script>
HOWEVER, when we look at our Adwords account it says to use this tag (with AW-):
<!-- Global site tag (gtag.js) - AdWords: 1234567890 --> <script async src="https://www.googletagmanager.com/gtag/js?id=AW-1234567890"></script>
<script>
window.dataLayer = window.dataLayer || [];
function gtag(){dataLayer.push(arguments);}
gtag('js', new Date());
gtag('config', 'AW-1234567890');
</script>
I've seen some videos and posts saying "if you're using either one of these, that's all you need". Is that true?
I have also seen a post that says you need two tags in it (UA- and AW-), as below:
<!-- Global site tag (gtag.js) - AdWords: 1234567890 --> <script async src="https://www.googletagmanager.com/gtag/js?id=AW-1234567890"></script>
<script>
window.dataLayer = window.dataLayer || [];
function gtag(){dataLayer.push(arguments);}
gtag('js', new Date());
gtag('config', 'AW-1234567890');
gtag('config', 'UA-1234567890');
</script>
I'd love to find out which is true, and as a result, which we should be using.
Thank you in advance for your assistance.

Answer 1

The last example you mention is the correct one. Anyway I would put the Google Analytics ID as a parameter as mentioned in the docs:
<script async src="https://www.googletagmanager.com/gtag/js?id=GA-PROPERTY_ID">
</script>
<script>
window.dataLayer = window.dataLayer || [];
function gtag(){dataLayer.push(arguments);}
gtag('js', new Date());
gtag('config', 'GA-PROPERTY_ID');
gtag('config', 'AW-GOOGLE_CONVERSION_ID');
</script>