A 1500 should be fine for you.
Your R730 can be configured in either redundant mode or non-redundant mode for power in the iDRAC settings. If you have it set up as redundant, it will use up to 750W (give or take a small amount for power conversion inefficiency and such) since a single power supply would need to be able to support the entire server if the other went down. In non-redundant mode, you can use up 1500W (again, give or take a small amount) but if one power supply goes down the entire system may go down (I’ve never personally tried this so not sure what actually happens).
You can also set a power cap in iDRAC settings as well if you want to be extra cautious - this is the maximum power it’ll use (give or take a small amount again).
I have a 1500W CyberPower unit that I use for my R730 with dual 750W power supplies (in redundant mode) along with several other things (other servers, networking equipment, tape drives, etc). I draw about 400-500W depending on what I’m doing. I don’t use any of the power capping features so theoretically I could exceed the maximum output of my UPS if I were to push all of my stuff to 100% usage but I never do that so it’s not an issue for me.
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