Observed supermassive black holes in the early universe have several proposed formation channels, in part because most of these channels are difficult to probe. One of the more promising channels, the directly collapse of a supermassive star, has several possible probes including the explosion of a helium supermassive star triggered by a general relativistic instability. We develop a straightforward method for evaluating the general relativistic radial instability without simplifying assumptions and apply it to population III supermassive stars taken from a post Newtonian stellar evolution code. This method finds that the instability occurs earlier in the evolutionary life of the star than according to previous methods. Using the stability analysis, we perform 1D general relativistic hydrodynamical simulations and find multiple general relativistic supernovae fueled by triple alpha and alpha capture reactions. The explosions, as well as several pulsations, occur in a lower and wider mass range (2.3e4-3.2e4 M$_\odot$) than had been suggested by previous works (5.5e4 M$_\odot$). We determine the explosion energy, velocity and ejecta composition, and compare the last of these to the abundances of observed metal poor stars. Because of the large explosion energy , these events should be visible to, among others, JWST.