yup you need a 3 prong, Positive Grid ditched the 2-prong a while ago and people have had to either contact PG for a replacement to swap out or they've found alternative PSU's on Amazon (should match the power requirements listed on the back of the Spark), and some have even switched over to using a battery for better portability

I found this cheap PSU in an old forum post, does 19V and enough current