But that's what a forum is good for - providing a detailed opinion on these instruments. The Rigol load in its current condition is not worth buying. I don't know when you purchased yours but the corresponding tests are online since ten months. The opinion on that product was fairly unison negative. Recommendations go in the direction of Maynuo, Itech or BK, or if you prefer a TFT screen maybe also Applent. These entry-level loads work faily well and are worth their money.
The DSA815 is a rather old design, though modernized at some time but definitely not the best bang-for-buck from a 2018 year's point of view. In this forum, you will probably be advised to look at the Siglent (can also be rusty...) SSA3021. These recommendations will be backed by many individuals who gained some common experience and make it available here for those looking for the best purchase in the instrument category/class they are about to get.
Moreover, decent T&M equipment distributors will offer a money-back period of a month or so, so in case one is really unhappy with the purchase, no worry, just send it back. If this is common in your country (Russia?) I don't know, but then a forum like this should be even more valuable.
Anyway, I understand your point of feeling offended by Rigol and that you won't buy any of their products in future. For comparison, there are other products of this manufacturer that apparently are decent quality though it also took them a while to get them right. I read few complaints from DS1000Z and DS2000A owners and the DP800 PSUs are also usable.
I hope you'll find a solution for the problem and that you'll finally be able to get the instruments that you're satisfied with.
Cheers,
Thomas