mac-minipowerusb
The cables from Apple come in only a 1 and 2 meter length. Can you use longer and still power the Mac Mini 2018 properly?
The Mac Mini 2018 according to the Apple website and AppleCare uses a
USB-C Charge Cable that is connected to a USB-C Power Adapter:
The picture in your question is referred to as an AC wall adapter, or "duckhead" (US) and slides out of the AC power adapter so you can then slide in the AC power cable (US), pictured in the link in your question.
The picture below shows the "duck head" being slid out of the AC power adapter and once removed the AC power cable gets slid in its place, thus providing an extension cord to the AC power adapter.
I do not think a simple cable to going to be sufficient. The differences between Thunderbolt and USB Type-C are different enough that an adapter will be needed. One such possible adapter would be the Kanex Thunderbolt Male to USB 3.1 (G2 Type-A) Female/ eSATA Female Adapter - Black. Unfortunately, this item is more expensive than anything mentioned in your question.
Another possible way to access the speed of a SSD would be to replace your internal drive. Although, these instructions show the upgrade procedure may be difficult.
Best Answer
No USB-C cable powers a Mac mini properly. USB is direct current, low voltage.