Combine water, sugar, and jalapeño rings in small saucepan over medium-high heat. Bring to a simmer then remove from heat and let steep in saucepan until completely cool.

In a shallow dish, whisk together margarita salt and chili powder.

Heat a grill (or grill pan) to medium-high, brush grill grates with oil. Char lime and jalapeño halves, cut-side down, until charred; transfer to a cutting board and juice 3 of the lime halves. Cut remaining lime half into wedges and slice jalapeño halves halfway up, lengthwise, for garnish; set aside.

Rub rim of two rocks glasses with charred lime wedges (or dip in water) and dip in Chili Margarita Salt to coat. Place two large square ice cubes in glasses, or fill with regular ice.

In a cocktail shaker filled with ice, combine 1½ ounces charred lime juice, tequila, orange liqueur, and simple syrup. Secure lid and shake vigorously until chilled. Double strain margarita into glasses, top each with a few dashes of bitters, and garnish with charred lime wedge and jalapeño half.