My understanding is that there is a bit of a hierarchy is "solving for X." If you file taxes and get refunds by Check, you get EIP as Check. Even if you get SS direct deposit. The EIP is first based on tax returns. It's like rock, paper, scissors.

Tax return 2019

Tax return 2018

SS or other benefit

Here is the card info:

https://www.eipcard.com/

And those of us signed up for e-newsletters have been getting this info for nearly a month. CFPB, for instance, mentions prepaid cards in the April 30 article:

https://www.consumerfinance.gov/about-us/blog/guide-covid-19-economic-stimulus-checks/