the smaller recepticle plug is a 30amp. the larger is a 50 amp. they do sell adapters for some 50 to 30amp services, but not all. there are alot of differant 50 amp plug configurations. if your welder came with that 50 amp plug, you better be sure to use a 50 amp service. you can burn your welder, burn your wiring if too small guage, or if your lucky, just trip the 30 amp breaker. your best bet here is to check your service panel and see if there is an open 220/240 and add a 50 amp breaker to it. use some #6 wire and mount a 50 amp recepticle in the garage so you have a dedicated 50 amp service for your welder. remember too to not use much electrical power through the rest of the house and garage while welding. air compressors, microwaves, even toasters use an amazing amount of amps. current draw will kill alot of electrical devices, not to mention burn up wires, which can cause fires. if you set your electrical supply up properly with large guage wires and all, you will notice your welds are MUCH better. proper penetration, and smoother pools. the welder will love you for it and last a long time.