They're are three power connectors in the "standard" family as defined by IEC...a low-, medium-, and high-current version. The low-current version is the one we're all used to, 10A. The one on some MicroVAX chassis is the 15A version. The third is a larger one (20A, I think but I'm not sure) that has three flat pins in a triangular arrangement but in two parallel planes, with a plain rectangular body. Tey're found on some larger Cisco routers (7513 for one) and on SGI Challenge-L systems for example.