Our PTA recently purchased a popcorn popper. It's 120V 15 amp with a three prong grounded plug but the two prongs are at 90 degrees of each other. This would fit into the t-slotted (I think it's called) 120V I've seen in new builds but this old school is just a standard three prong where the 2 prongs are parallel. What are my options? Do I need to get a outlet replaced or is there a converter out there? HELP please!

As long as the building wiring is #12, then the apparent 15 amp receptacle can be changed to a 20 amp device, which is the T slot device.

I will not recommend an adapter for a commercial popcorn popper. Most of the power used is from the electric heating elements, and they cause plug connections to heat up excessively quickly.