Any valid SSL certificate will do, as long as it is designed to protect web pages (i.e NOT "Code Signing Certificates" or "Email validation Certificates").
e.g. Visit:
http://www.c1-domains.com -> click on SSL certificates -> Select See all Certificates:
Any of those three types will work, even the cheapest "Standard SSL Certificate".
**** Disclosure: We generate income from
www.c1-domains.com. Shop around to see what the alternatives are and what they cost. There are literally 100s of companies and resellers offering SSL certificates and many will be cheaper than ours.
Essentially, in Plesk (Servers -> Certificates) you Add New Certificate, fill in the form at the top, and click on the Request button. *** You must use the full domain, if necessary including the www in the "Domain Name" box. For example if your customers visit
https://www.myhostingcompanyname.com:8443 to get to Plesk then you should enter
www.myhostingcompanyname.com in the Domain Name box ***. Also be sure to select 1024 bits not 512 or 2048.
Doing the above generates a CSR ( = Certificate Signing Request, I think) which is a block of gibberish text. You then copy it and then past into the appropriate box on the SSL certificate signup web page during the signup process. You pay your money, then you get two things back: The certificate itself and usually what's known as a "CA Certificate".
Back in Plesk, go to the certificate you just created and paste these things into the appropriate boxes and click on Send Text
All being well you should get no errors, and the certificate should show up in the list of certificates (Server -> Certificates) with all its parts (CA, Certificate) shown as being present (gold coloured icons rather then grayed out ones). Put a check in the box next to it, and click on Secure Control Panel just above the list.
You may need to restart Plesk (service psa restart) in order to get the new certificate working.
You can see if it is the right one if get no errors when logging in. If you still get errors, in Internet Explorer click on File -> Properties -> click on Certificate to see what's happening (and similarly for FF or Safari or whatever)
Hope this helps.
Faris.