It doesn't actually make a difference.
"dc", properly capitalized as "DC", refers to direct current. So 1.3 V DC simply means that the required RAM runs using 1.3 volts of direct current. (If you don't know about direct vs. alternating current, you can read about the differences here).
Now, if you look at the power cable that's probably attached to your computer, there'll be a brick somewhere in the middle of it. That brick is the AC transadapter, which is a combination of an adapter and a transformer. It performs the function of transforming the incoming power down to a lower voltage that's safe for the computer (usually 12 V, though it can vary), and then adapting the AC current that comes from the socket outlet and through the transformer into DC current, because that's what computers work on.
That's important because it means that any type of RAM runs on DC. Even if something specified AC for some RAM, the RAM wouldn't get AC because the only power coming into the computer and components is DC. Hence, a RAM package that's specified 1.3 V is no different in terms of power requirements from another that's specified 1.3 V DC.