A 128GB card will allow you to load EVERY 8-bit and 16-bit game out there, all of the arcade games that work, and quite a few PS1, Dreamcast, PSP, and Sega CD games (those systems have the largest file sizes). In general, I would expect to pay $7 for a 16GB card, $20 for a 128GB card, and $30 for a 256GB card. The prices fluctuate all the time, so keep an eye out for deals. In general, I recommend the cards listed below, in order or preference.

I recommend you store that original card somewhere safe in case you run into any issues in the future, and buy new SD cards from a reputable brand like SanDisk or Samsung to use in your device. Your safest bet is to replace your cards with microSD cards from a well-known brand. The “TF2” slot is for your game files, so you will want a larger card for that one. The “TF1” slot on your device holds the system firmware, so for that card 16GB is ideal. The RG351V will come bundled with a single microSD card, and in some cases two SD cards, but they are from a generic brand and will be prone to failure.

Sandisk (left) and Samsung (right) microSD cards