If you have a list of the hosts, the hosts must have either single quotes, or double-quotes around them. If they're already comma-separated, this will be easy to do in Excel.
Select the cells, in the Home tab, select Format→Format Cells. Choose Custom, and in the Type text box, enter: '@'.
If the list of hosts you have are in a column instead of a row, select the individual cells in the column (not the column itself) and copy them, make a new Excel file, or a new sheet. Click the paste icon, and choose Transpose Paste.
Save the file and open it with a text editor. The hostnames should now all have quotes around them, and comma-separated. Copy the text.
Create a variable in Powershell (in this script, it's default computers) and make it equal to the pasted comma-separated, enclosed in single-quotes hostnames. Run the script. You will get a table output like below (results obfuscated):