Most all wall plugs in North America are type A or type B.
What type of cable end usually plugs into an aftermarket PSU?
I am pretty sure it is the C13 cable, but not many PSUs make this specification.
I am asking because I am hoping to purchase an HP E7681-63001 PDU, plug it into my 30A dryer plug, and plug 4 * 1,400 PSUs into it. I assume I will need 4*male-female c13 cables to do so. Am I right?
The C13 (often referred to in industry as an IEC cable) is an absolute standard for computer PSU mains connections. Cables with 15A north american mains (NEMA 5/type B) male end* and IEC female end are thus ubiquitous. Note that the HP PDU, since it's intended for direct use with computer equipment, features female IEC connectors. So you need an IEC->IEC cable (commonly referred to as IEC Extension) rather than a mains->IEC cable to connect devices to this PDU. These cables are a little less common, but still cheap.
Note that the dryer receptacle you have now (probably a NEMA 14) will not be matched by the connector that comes with the PDU, since data centers almost universally use the NEMA L-series "twist-lok" connectors for mains service. So, you'll need to splice on a new cable, which you should be careful with since this will carry around 240v 20A (plus or minus a lot, depending on machine load) in the configuration you describe. In an enterprise environment any non-locking connector is considered a hazard (unreliable, unsafe), and I think this should be wisely carried to homes. What I'm saying is that it might be worth it to have a twist-lok connector installed.
(*) In the theatre industry we call these Edison plugs. I'm not sure how common the term is in IT. There are a lot of standards that define these plugs, NEMA 5 is cited the most.
Yes, I have yet to encounter a consumer market PC made in the last 20 years that doesn't use the C13 cable in the back. It may not be stated on the spec sheet, but its so ubiquitous it may as well be assumed.
