Connecting 13 inch 2018 MacBookPro to Dell U2417h
If you want to be able to charge your laptop at the same time, you'll can use a Thunderbolt 3 dock or hub to connect the two monitors at the same time as well as charging through a single port on your laptop - leaving one port available for charging.

A product that will allow you to do this could be the OWC Thunderbolt 3 dock:

https://www.owcdigital.com/products/thunderbolt-3-dock-14-port

You would then connect your existing monitor using your existing cable to the dock. use a mini-Displayport to DisplayPort cable to connect your U2417H monitor to the dock. The dock comes with a Thunderbolt 3 cable that connects the laptop to the dock. The dock provides charging to the laptop.

There exist similar products at various price points from several other brands.

If you want to use your existing dongle you can simply connect your charger to the dongle, connect the dongle to the laptop and use an HDMI-to-HDMI cable to connect the U2417H monitor. The existing monitor uses the same cable as before.

This is obviously much cheaper for you, but you'll need to plug two cables into the laptop leaving no ports free for other uses.